[PATCH v6 0/3] riscv/ptrace: add new regset to access original a0 register

[PATCH v6 0/3] riscv/ptrace: add new regset to access original a0 register

[Celeste Liu]

The orig_a0 is missing in struct user_regs_struct of riscv, and there is
no way to add it without breaking UAPI. (See Link tag below)

Like NT_ARM_SYSTEM_CALL do, we add a new regset name NT_RISCV_ORIG_A0 to
access original a0 register from userspace via ptrace API.

Link: https://lore.kernel.org/all/59505464-c84a-403d-972f-d4b2055eeaac@gmail.com/

Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
---
Changes in v6:
- Fix obsolute comment.
- Copy include/linux/stddef.h to tools/include to use offsetofend in
  selftests.
- Link to v5: https://lore.kernel.org/r/20250115-riscv-new-regset-v5-0-d0e6ec031a23@coelacanthus.name

Changes in v5:
- Fix wrong usage in selftests.
- Link to v4: https://lore.kernel.org/r/20241226-riscv-new-regset-v4-0-4496a29d0436@coelacanthus.name

Changes in v4:
- Fix a copy paste error in selftest. (Forget to commit...)
- Link to v3: https://lore.kernel.org/r/20241226-riscv-new-regset-v3-0-f5b96465826b@coelacanthus.name

Changes in v3:
- Use return 0 directly for readability.
- Fix test for modify a0.
- Add Fixes: tag
- Remove useless Cc: stable.
- Selftest will check both a0 and orig_a0, but depends on the
  correctness of PTRACE_GET_SYSCALL_INFO.
- Link to v2: https://lore.kernel.org/r/20241203-riscv-new-regset-v2-0-d37da8c0cba6@coelacanthus.name

Changes in v2:
- Fix integer width.
- Add selftest.
- Link to v1: https://lore.kernel.org/r/20241201-riscv-new-regset-v1-1-c83c58abcc7b@coelacanthus.name

---
Celeste Liu (3):
      riscv/ptrace: add new regset to access original a0 register
      tools: copy include/linux/stddef.h to tools/include
      riscv: selftests: Add a ptrace test to verify a0 and orig_a0 access

 arch/riscv/kernel/ptrace.c                   |  32 +++++
 include/uapi/linux/elf.h                     |   1 +
 tools/include/linux/stddef.h                 |  85 ++++++++++++
 tools/include/uapi/linux/stddef.h            |   6 +-
 tools/testing/selftests/riscv/abi/.gitignore |   1 +
 tools/testing/selftests/riscv/abi/Makefile   |   6 +-
 tools/testing/selftests/riscv/abi/ptrace.c   | 193 +++++++++++++++++++++++++++
 7 files changed, 319 insertions(+), 5 deletions(-)
---
base-commit: 0e287d31b62bb53ad81d5e59778384a40f8b6f56
change-id: 20241201-riscv-new-regset-d529b952ad0d

Best regards,
-- 
Celeste Liu <uwu@coelacanthus.name>

[PATCH v6 1/3] riscv/ptrace: add new regset to access original a0 register

[Celeste Liu]

The orig_a0 is missing in struct user_regs_struct of riscv, and there is
no way to add it without breaking UAPI. (See Link tag below)

Like NT_ARM_SYSTEM_CALL do, we add a new regset name NT_RISCV_ORIG_A0 to
access original a0 register from userspace via ptrace API.

Fixes: e2c0cdfba7f6 ("RISC-V: User-facing API")
Link: https://lore.kernel.org/all/59505464-c84a-403d-972f-d4b2055eeaac@gmail.com/
Cc: stable@vger.kernel.org
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
---
 arch/riscv/kernel/ptrace.c | 32 ++++++++++++++++++++++++++++++++
 include/uapi/linux/elf.h   |  1 +
 2 files changed, 33 insertions(+)

diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
index ea67e9fb7a583683b922fe2c017ea61f3bc848db..ef9ab74c8575a5c440155973b1c625c06a867c97 100644
--- a/arch/riscv/kernel/ptrace.c
+++ b/arch/riscv/kernel/ptrace.c
@@ -31,6 +31,7 @@ enum riscv_regset {
 #ifdef CONFIG_RISCV_ISA_SUPM
 	REGSET_TAGGED_ADDR_CTRL,
 #endif
+	REGSET_ORIG_A0,
 };
 
 static int riscv_gpr_get(struct task_struct *target,
@@ -184,6 +185,29 @@ static int tagged_addr_ctrl_set(struct task_struct *target,
 }
 #endif
 
+static int riscv_orig_a0_get(struct task_struct *target,
+			     const struct user_regset *regset,
+			     struct membuf to)
+{
+	return membuf_store(&to, task_pt_regs(target)->orig_a0);
+}
+
+static int riscv_orig_a0_set(struct task_struct *target,
+			     const struct user_regset *regset,
+			     unsigned int pos, unsigned int count,
+			     const void *kbuf, const void __user *ubuf)
+{
+	unsigned long orig_a0 = task_pt_regs(target)->orig_a0;
+	int ret;
+
+	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &orig_a0, 0, -1);
+	if (ret)
+		return ret;
+
+	task_pt_regs(target)->orig_a0 = orig_a0;
+	return 0;
+}
+
 static const struct user_regset riscv_user_regset[] = {
 	[REGSET_X] = {
 		.core_note_type = NT_PRSTATUS,
@@ -224,6 +248,14 @@ static const struct user_regset riscv_user_regset[] = {
 		.set = tagged_addr_ctrl_set,
 	},
 #endif
+	[REGSET_ORIG_A0] = {
+		.core_note_type = NT_RISCV_ORIG_A0,
+		.n = 1,
+		.size = sizeof(elf_greg_t),
+		.align = sizeof(elf_greg_t),
+		.regset_get = riscv_orig_a0_get,
+		.set = riscv_orig_a0_set,
+	},
 };
 
 static const struct user_regset_view riscv_user_native_view = {
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index b44069d29cecc0f9de90ee66bfffd2137f4275a8..390060229601631da2fb27030d9fa2142e676c14 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -452,6 +452,7 @@ typedef struct elf64_shdr {
 #define NT_RISCV_CSR	0x900		/* RISC-V Control and Status Registers */
 #define NT_RISCV_VECTOR	0x901		/* RISC-V vector registers */
 #define NT_RISCV_TAGGED_ADDR_CTRL 0x902	/* RISC-V tagged address control (prctl()) */
+#define NT_RISCV_ORIG_A0	  0x903	/* RISC-V original a0 register */
 #define NT_LOONGARCH_CPUCFG	0xa00	/* LoongArch CPU config registers */
 #define NT_LOONGARCH_CSR	0xa01	/* LoongArch control and status registers */
 #define NT_LOONGARCH_LSX	0xa02	/* LoongArch Loongson SIMD Extension registers */

-- 
2.48.0

[PATCH v6 2/3] tools: copy include/linux/stddef.h to tools/include

[Celeste Liu]

Some macro defined in stddef.h are useful and have been used in many
code in selftests. Copy them to tools/include so developers needn't
create their copy in every files.

Remove some definitions like NULL and true/false to be suitable to
non-kernel environment.

Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
---
 tools/include/linux/stddef.h      | 85 +++++++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/stddef.h |  6 +--
 2 files changed, 87 insertions(+), 4 deletions(-)

diff --git a/tools/include/linux/stddef.h b/tools/include/linux/stddef.h
new file mode 100644
index 0000000000000000000000000000000000000000..55f3964d9a3d9f9f9345a75248eec027c56faef9
--- /dev/null
+++ b/tools/include/linux/stddef.h
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_STDDEF_H
+#define _LINUX_STDDEF_H
+
+#include <uapi/linux/stddef.h>
+
+/**
+ * sizeof_field() - Report the size of a struct field in bytes
+ *
+ * @TYPE: The structure containing the field of interest
+ * @MEMBER: The field to return the size of
+ */
+#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
+
+/**
+ * offsetofend() - Report the offset of a struct field within the struct
+ *
+ * @TYPE: The type of the structure
+ * @MEMBER: The member within the structure to get the end offset of
+ */
+#define offsetofend(TYPE, MEMBER) \
+	(offsetof(TYPE, MEMBER)	+ sizeof_field(TYPE, MEMBER))
+
+/**
+ * struct_group() - Wrap a set of declarations in a mirrored struct
+ *
+ * @NAME: The identifier name of the mirrored sub-struct
+ * @MEMBERS: The member declarations for the mirrored structs
+ *
+ * Used to create an anonymous union of two structs with identical
+ * layout and size: one anonymous and one named. The former can be
+ * used normally without sub-struct naming, and the latter can be
+ * used to reason about the start, end, and size of the group of
+ * struct members.
+ */
+#define struct_group(NAME, MEMBERS...)	\
+	__struct_group(/* no tag */, NAME, /* no attrs */, MEMBERS)
+
+/**
+ * struct_group_attr() - Create a struct_group() with trailing attributes
+ *
+ * @NAME: The identifier name of the mirrored sub-struct
+ * @ATTRS: Any struct attributes to apply
+ * @MEMBERS: The member declarations for the mirrored structs
+ *
+ * Used to create an anonymous union of two structs with identical
+ * layout and size: one anonymous and one named. The former can be
+ * used normally without sub-struct naming, and the latter can be
+ * used to reason about the start, end, and size of the group of
+ * struct members. Includes structure attributes argument.
+ */
+#define struct_group_attr(NAME, ATTRS, MEMBERS...) \
+	__struct_group(/* no tag */, NAME, ATTRS, MEMBERS)
+
+/**
+ * struct_group_tagged() - Create a struct_group with a reusable tag
+ *
+ * @TAG: The tag name for the named sub-struct
+ * @NAME: The identifier name of the mirrored sub-struct
+ * @MEMBERS: The member declarations for the mirrored structs
+ *
+ * Used to create an anonymous union of two structs with identical
+ * layout and size: one anonymous and one named. The former can be
+ * used normally without sub-struct naming, and the latter can be
+ * used to reason about the start, end, and size of the group of
+ * struct members. Includes struct tag argument for the named copy,
+ * so the specified layout can be reused later.
+ */
+#define struct_group_tagged(TAG, NAME, MEMBERS...) \
+	__struct_group(TAG, NAME, /* no attrs */, MEMBERS)
+
+/**
+ * DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
+ *
+ * @TYPE: The type of each flexible array element
+ * @NAME: The name of the flexible array member
+ *
+ * In order to have a flexible array member in a union or alone in a
+ * struct, it needs to be wrapped in an anonymous struct with at least 1
+ * named member, but that member can be empty.
+ */
+#define DECLARE_FLEX_ARRAY(TYPE, NAME) \
+	__DECLARE_FLEX_ARRAY(TYPE, NAME)
+
+#endif
diff --git a/tools/include/uapi/linux/stddef.h b/tools/include/uapi/linux/stddef.h
index bb6ea517efb51177a7983fadad9b590b12b786e5..f2548fd95f6e1d8cb218d52918bb81a3317d10b1 100644
--- a/tools/include/uapi/linux/stddef.h
+++ b/tools/include/uapi/linux/stddef.h
@@ -1,8 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
-#ifndef _LINUX_STDDEF_H
-#define _LINUX_STDDEF_H
-
-
+#ifndef _UAPI_LINUX_STDDEF_H
+#define _UAPI_LINUX_STDDEF_H
 
 #ifndef __always_inline
 #define __always_inline __inline__

-- 
2.48.0

[PATCH v6 3/3] riscv: selftests: Add a ptrace test to verify a0 and orig_a0 access

[Celeste Liu]

This test checks that orig_a0 and a0 can be modified and accessed
independently.

Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Co-developed-by: Charlie Jenkins <charlie@rivosinc.com>
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
---
 tools/testing/selftests/riscv/abi/.gitignore |   1 +
 tools/testing/selftests/riscv/abi/Makefile   |   6 +-
 tools/testing/selftests/riscv/abi/ptrace.c   | 193 +++++++++++++++++++++++++++
 3 files changed, 199 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/riscv/abi/.gitignore b/tools/testing/selftests/riscv/abi/.gitignore
index b38358f91c4d2240ae64892871d9ca98bda1ae58..378c605919a3b3d58eec2701eb7af430cfe315d6 100644
--- a/tools/testing/selftests/riscv/abi/.gitignore
+++ b/tools/testing/selftests/riscv/abi/.gitignore
@@ -1 +1,2 @@
 pointer_masking
+ptrace
diff --git a/tools/testing/selftests/riscv/abi/Makefile b/tools/testing/selftests/riscv/abi/Makefile
index ed82ff9c664e7eb3f760cbab81fb957ff72579c5..359a082c88a401883fb3776b35e4dacf69beaaaa 100644
--- a/tools/testing/selftests/riscv/abi/Makefile
+++ b/tools/testing/selftests/riscv/abi/Makefile
@@ -1,10 +1,14 @@
 # SPDX-License-Identifier: GPL-2.0
 
 CFLAGS += -I$(top_srcdir)/tools/include
+CFLAGS += $(KHDR_INCLUDES)
 
-TEST_GEN_PROGS := pointer_masking
+TEST_GEN_PROGS := pointer_masking ptrace
 
 include ../../lib.mk
 
 $(OUTPUT)/pointer_masking: pointer_masking.c
 	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
+
+$(OUTPUT)/ptrace: ptrace.c
+	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
diff --git a/tools/testing/selftests/riscv/abi/ptrace.c b/tools/testing/selftests/riscv/abi/ptrace.c
new file mode 100644
index 0000000000000000000000000000000000000000..cbd60462021165ca2bcc38be24b8423c96047b93
--- /dev/null
+++ b/tools/testing/selftests/riscv/abi/ptrace.c
@@ -0,0 +1,193 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/ptrace.h>
+#include <sys/stat.h>
+#include <sys/user.h>
+#include <sys/wait.h>
+#include <sys/uio.h>
+#include <linux/elf.h>
+#include <linux/unistd.h>
+#include <linux/ptrace.h>
+#include <linux/stddef.h>
+#include <asm/ptrace.h>
+
+#include "../../kselftest_harness.h"
+
+#define ORIG_A0_MODIFY      0x01
+#define A0_MODIFY           0x02
+#define A0_OLD              0xbadbeefbeeff
+#define A0_NEW              0xffeebfeebdab
+
+
+struct a0_regs {
+	__s64 orig_a0;
+	__u64 a0;
+};
+
+#define perr_and_exit(fmt, ...)						\
+	({								\
+		char buf[256];						\
+		snprintf(buf, sizeof(buf), "%s:%d:" fmt ": %m\n",	\
+			__func__, __LINE__, ##__VA_ARGS__);		\
+		ksft_exit_fail_perror(buf);				\
+	})
+
+static void ptrace_test(int opt, struct a0_regs result[])
+{
+	int status;
+	long rc;
+	pid_t pid;
+	struct user_regs_struct regs;
+	struct iovec iov = {
+		.iov_base = &regs,
+		.iov_len = sizeof(regs),
+	};
+
+	unsigned long orig_a0;
+	struct iovec a0_iov = {
+		.iov_base = &orig_a0,
+		.iov_len = sizeof(orig_a0),
+	};
+	struct ptrace_syscall_info syscall_info = {
+		.op = 0xff,
+	};
+	const unsigned int expected_sci_entry_size =
+		offsetofend(struct ptrace_syscall_info, entry.args);
+	const unsigned int expected_sci_exit_size =
+		offsetofend(struct ptrace_syscall_info, exit.is_error);
+
+	pid = fork();
+	if (pid == 0) {
+		/* Mark oneself being traced */
+		long val = ptrace(PTRACE_TRACEME, 0, 0, 0);
+
+		if (val < 0)
+			perr_and_exit("failed to request for tracer to trace me: %ld", val);
+
+		kill(getpid(), SIGSTOP);
+
+		/* Perform chdir syscall that will be intercepted */
+		syscall(__NR_chdir, A0_OLD);
+
+		exit(0);
+	}
+
+	if (pid < 0)
+		ksft_exit_fail_perror("failed to fork");
+
+	for (int i = 0; i < 3; i++) {
+		if (waitpid(pid, &status, 0) != pid)
+			perr_and_exit("failed to wait for the tracee %d", pid);
+		if (WIFSTOPPED(status)) {
+			switch (WSTOPSIG(status)) {
+			case SIGSTOP:
+				if (ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_TRACESYSGOOD) < 0)
+					perr_and_exit("failed to set PTRACE_O_TRACESYSGOOD");
+				break;
+			case SIGTRAP|0x80:
+				/* Modify twice so GET_SYSCALL_INFO get modified a0 and orig_a0 */
+				if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
+					perr_and_exit("failed to get tracee registers");
+				if (ptrace(PTRACE_GETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
+					perr_and_exit("failed to get tracee registers");
+
+				/* Modify a0/orig_a0 for the syscall */
+				switch (opt) {
+				case A0_MODIFY:
+					regs.a0 = A0_NEW;
+					break;
+				case ORIG_A0_MODIFY:
+					orig_a0 = A0_NEW;
+					break;
+				}
+
+				if (ptrace(PTRACE_SETREGSET, pid, NT_PRSTATUS, &iov))
+					perr_and_exit("failed to set tracee registers");
+				if (ptrace(PTRACE_SETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
+					perr_and_exit("failed to set tracee registers");
+				switch (i) {
+				case 1:
+					/* Stop at the beginning of syscall */
+					rc = ptrace(PTRACE_GET_SYSCALL_INFO, pid,
+						sizeof(syscall_info), &syscall_info);
+					if (rc < 0)
+						perr_and_exit("failed to get syscall info of entry");
+					if (rc < expected_sci_entry_size
+						|| syscall_info.op != PTRACE_SYSCALL_INFO_ENTRY)
+						perr_and_exit("stop position of entry mismatched");
+					result[0].orig_a0 = syscall_info.entry.args[0];
+					break;
+
+				case 2:
+					/* Stop at the end of syscall */
+					rc = ptrace(PTRACE_GET_SYSCALL_INFO, pid,
+						sizeof(syscall_info), &syscall_info);
+					if (rc < 0)
+						perr_and_exit("failed to get syscall info of entry");
+					if (rc < expected_sci_exit_size
+						|| syscall_info.op != PTRACE_SYSCALL_INFO_EXIT)
+						perr_and_exit("stop position of exit mismatched");
+					result[0].a0 = syscall_info.exit.rval;
+
+					if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
+						perr_and_exit("failed to get tracee registers");
+					result[1].a0 = regs.a0;
+					if (ptrace(PTRACE_GETREGSET, pid, NT_RISCV_ORIG_A0,
+						   &a0_iov))
+						perr_and_exit("failed to get tracee registers");
+					result[1].orig_a0 = orig_a0;
+				}
+			}
+			if (ptrace(PTRACE_SYSCALL, pid, 0, 0) < 0)
+				perr_and_exit("failed to resume tracee");
+		}
+	}
+
+	/* Resume the tracee */
+	ptrace(PTRACE_CONT, pid, 0, 0);
+	if (waitpid(pid, &status, 0) != pid)
+		perr_and_exit("failed to wait for the tracee");
+
+}
+
+TEST(ptrace_access_a0)
+{
+	struct a0_regs result[2];
+
+	ptrace_test(A0_MODIFY, result);
+
+	/* Verify PTRACE_SETREGSET */
+	/* The modification of a0 cannot affect the first argument of the syscall */
+	EXPECT_EQ(A0_OLD, result[0].orig_a0);
+	EXPECT_EQ(A0_NEW, result[0].a0);
+
+	/* Verify PTRACE_GETREGSET */
+	EXPECT_EQ(result[1].orig_a0, result[0].orig_a0);
+	EXPECT_EQ(result[1].a0, result[0].a0);
+}
+
+TEST(ptrace_access_orig_a0)
+{
+	struct a0_regs result[2];
+
+	ptrace_test(ORIG_A0_MODIFY, result);
+
+	/* Verify PTRACE_SETREGSET */
+	/* Only modify orig_a0 to change the first argument of the syscall */
+	EXPECT_EQ(A0_NEW, result[0].orig_a0);
+	/* a0 will not be affected */
+	EXPECT_NE(A0_NEW, result[0].a0);
+
+	/* Verify PTRACE_GETREGSET */
+	EXPECT_EQ(result[1].orig_a0, result[0].orig_a0);
+	EXPECT_EQ(result[1].a0, result[0].a0);
+}
+
+TEST_HARNESS_MAIN

-- 
2.48.0

Re: [PATCH v6 2/3] tools: copy include/linux/stddef.h to tools/include

[Andrew Jones]

On Wed, Jan 15, 2025 at 07:13:28PM +0800, Celeste Liu wrote:
> Some macro defined in stddef.h are useful and have been used in many
> code in selftests. Copy them to tools/include so developers needn't
> create their copy in every files.
> 
> Remove some definitions like NULL and true/false to be suitable to
> non-kernel environment.
> 
> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
> ---
>  tools/include/linux/stddef.h      | 85 +++++++++++++++++++++++++++++++++++++++
>  tools/include/uapi/linux/stddef.h |  6 +--
>  2 files changed, 87 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/include/linux/stddef.h b/tools/include/linux/stddef.h
> new file mode 100644
> index 0000000000000000000000000000000000000000..55f3964d9a3d9f9f9345a75248eec027c56faef9
> --- /dev/null
> +++ b/tools/include/linux/stddef.h
> @@ -0,0 +1,85 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_STDDEF_H
> +#define _LINUX_STDDEF_H
> +
> +#include <uapi/linux/stddef.h>
> +
> +/**
> + * sizeof_field() - Report the size of a struct field in bytes
> + *
> + * @TYPE: The structure containing the field of interest
> + * @MEMBER: The field to return the size of
> + */
> +#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
> +
> +/**
> + * offsetofend() - Report the offset of a struct field within the struct
> + *
> + * @TYPE: The type of the structure
> + * @MEMBER: The member within the structure to get the end offset of
> + */
> +#define offsetofend(TYPE, MEMBER) \
> +	(offsetof(TYPE, MEMBER)	+ sizeof_field(TYPE, MEMBER))
> +
> +/**
> + * struct_group() - Wrap a set of declarations in a mirrored struct
> + *
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical
> + * layout and size: one anonymous and one named. The former can be
> + * used normally without sub-struct naming, and the latter can be
> + * used to reason about the start, end, and size of the group of
> + * struct members.
> + */
> +#define struct_group(NAME, MEMBERS...)	\
> +	__struct_group(/* no tag */, NAME, /* no attrs */, MEMBERS)
> +
> +/**
> + * struct_group_attr() - Create a struct_group() with trailing attributes
> + *
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @ATTRS: Any struct attributes to apply
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical
> + * layout and size: one anonymous and one named. The former can be
> + * used normally without sub-struct naming, and the latter can be
> + * used to reason about the start, end, and size of the group of
> + * struct members. Includes structure attributes argument.
> + */
> +#define struct_group_attr(NAME, ATTRS, MEMBERS...) \
> +	__struct_group(/* no tag */, NAME, ATTRS, MEMBERS)
> +
> +/**
> + * struct_group_tagged() - Create a struct_group with a reusable tag
> + *
> + * @TAG: The tag name for the named sub-struct
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical
> + * layout and size: one anonymous and one named. The former can be
> + * used normally without sub-struct naming, and the latter can be
> + * used to reason about the start, end, and size of the group of
> + * struct members. Includes struct tag argument for the named copy,
> + * so the specified layout can be reused later.
> + */
> +#define struct_group_tagged(TAG, NAME, MEMBERS...) \
> +	__struct_group(TAG, NAME, /* no attrs */, MEMBERS)
> +
> +/**
> + * DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
> + *
> + * @TYPE: The type of each flexible array element
> + * @NAME: The name of the flexible array member
> + *
> + * In order to have a flexible array member in a union or alone in a
> + * struct, it needs to be wrapped in an anonymous struct with at least 1
> + * named member, but that member can be empty.
> + */
> +#define DECLARE_FLEX_ARRAY(TYPE, NAME) \
> +	__DECLARE_FLEX_ARRAY(TYPE, NAME)
> +
> +#endif
> diff --git a/tools/include/uapi/linux/stddef.h b/tools/include/uapi/linux/stddef.h
> index bb6ea517efb51177a7983fadad9b590b12b786e5..f2548fd95f6e1d8cb218d52918bb81a3317d10b1 100644
> --- a/tools/include/uapi/linux/stddef.h
> +++ b/tools/include/uapi/linux/stddef.h
> @@ -1,8 +1,6 @@
>  /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> -#ifndef _LINUX_STDDEF_H
> -#define _LINUX_STDDEF_H
> -
> -
> +#ifndef _UAPI_LINUX_STDDEF_H
> +#define _UAPI_LINUX_STDDEF_H
>  
>  #ifndef __always_inline
>  #define __always_inline __inline__
> 
> -- 
> 2.48.0
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Re: [PATCH v6 3/3] riscv: selftests: Add a ptrace test to verify a0 and orig_a0 access

[Andrew Jones]

On Wed, Jan 15, 2025 at 07:13:29PM +0800, Celeste Liu wrote:
> This test checks that orig_a0 and a0 can be modified and accessed
> independently.
> 
> Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
> Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
> Co-developed-by: Charlie Jenkins <charlie@rivosinc.com>
> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
> ---
>  tools/testing/selftests/riscv/abi/.gitignore |   1 +
>  tools/testing/selftests/riscv/abi/Makefile   |   6 +-
>  tools/testing/selftests/riscv/abi/ptrace.c   | 193 +++++++++++++++++++++++++++
>  3 files changed, 199 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/riscv/abi/.gitignore b/tools/testing/selftests/riscv/abi/.gitignore
> index b38358f91c4d2240ae64892871d9ca98bda1ae58..378c605919a3b3d58eec2701eb7af430cfe315d6 100644
> --- a/tools/testing/selftests/riscv/abi/.gitignore
> +++ b/tools/testing/selftests/riscv/abi/.gitignore
> @@ -1 +1,2 @@
>  pointer_masking
> +ptrace
> diff --git a/tools/testing/selftests/riscv/abi/Makefile b/tools/testing/selftests/riscv/abi/Makefile
> index ed82ff9c664e7eb3f760cbab81fb957ff72579c5..359a082c88a401883fb3776b35e4dacf69beaaaa 100644
> --- a/tools/testing/selftests/riscv/abi/Makefile
> +++ b/tools/testing/selftests/riscv/abi/Makefile
> @@ -1,10 +1,14 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
>  CFLAGS += -I$(top_srcdir)/tools/include
> +CFLAGS += $(KHDR_INCLUDES)
>  
> -TEST_GEN_PROGS := pointer_masking
> +TEST_GEN_PROGS := pointer_masking ptrace
>  
>  include ../../lib.mk
>  
>  $(OUTPUT)/pointer_masking: pointer_masking.c
>  	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
> +
> +$(OUTPUT)/ptrace: ptrace.c
> +	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
> diff --git a/tools/testing/selftests/riscv/abi/ptrace.c b/tools/testing/selftests/riscv/abi/ptrace.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..cbd60462021165ca2bcc38be24b8423c96047b93
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/abi/ptrace.c
> @@ -0,0 +1,193 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <fcntl.h>
> +#include <signal.h>
> +#include <errno.h>
> +#include <sys/types.h>
> +#include <sys/ptrace.h>
> +#include <sys/stat.h>
> +#include <sys/user.h>
> +#include <sys/wait.h>
> +#include <sys/uio.h>
> +#include <linux/elf.h>
> +#include <linux/unistd.h>
> +#include <linux/ptrace.h>
> +#include <linux/stddef.h>
> +#include <asm/ptrace.h>
> +
> +#include "../../kselftest_harness.h"
> +
> +#define ORIG_A0_MODIFY      0x01
> +#define A0_MODIFY           0x02
> +#define A0_OLD              0xbadbeefbeeff
> +#define A0_NEW              0xffeebfeebdab
> +
> +
> +struct a0_regs {
> +	__s64 orig_a0;
> +	__u64 a0;
> +};
> +
> +#define perr_and_exit(fmt, ...)						\
> +	({								\
> +		char buf[256];						\
> +		snprintf(buf, sizeof(buf), "%s:%d:" fmt ": %m\n",	\
> +			__func__, __LINE__, ##__VA_ARGS__);		\
> +		ksft_exit_fail_perror(buf);				\
> +	})
> +
> +static void ptrace_test(int opt, struct a0_regs result[])
> +{
> +	int status;
> +	long rc;
> +	pid_t pid;
> +	struct user_regs_struct regs;
> +	struct iovec iov = {
> +		.iov_base = &regs,
> +		.iov_len = sizeof(regs),
> +	};
> +
> +	unsigned long orig_a0;
> +	struct iovec a0_iov = {
> +		.iov_base = &orig_a0,
> +		.iov_len = sizeof(orig_a0),
> +	};
> +	struct ptrace_syscall_info syscall_info = {
> +		.op = 0xff,
> +	};
> +	const unsigned int expected_sci_entry_size =
> +		offsetofend(struct ptrace_syscall_info, entry.args);
> +	const unsigned int expected_sci_exit_size =
> +		offsetofend(struct ptrace_syscall_info, exit.is_error);
> +
> +	pid = fork();
> +	if (pid == 0) {
> +		/* Mark oneself being traced */
> +		long val = ptrace(PTRACE_TRACEME, 0, 0, 0);
> +
> +		if (val < 0)
> +			perr_and_exit("failed to request for tracer to trace me: %ld", val);
> +
> +		kill(getpid(), SIGSTOP);
> +
> +		/* Perform chdir syscall that will be intercepted */
> +		syscall(__NR_chdir, A0_OLD);
> +
> +		exit(0);
> +	}
> +
> +	if (pid < 0)
> +		ksft_exit_fail_perror("failed to fork");
> +
> +	for (int i = 0; i < 3; i++) {
> +		if (waitpid(pid, &status, 0) != pid)
> +			perr_and_exit("failed to wait for the tracee %d", pid);
> +		if (WIFSTOPPED(status)) {
> +			switch (WSTOPSIG(status)) {
> +			case SIGSTOP:
> +				if (ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_TRACESYSGOOD) < 0)
> +					perr_and_exit("failed to set PTRACE_O_TRACESYSGOOD");
> +				break;
> +			case SIGTRAP|0x80:
> +				/* Modify twice so GET_SYSCALL_INFO get modified a0 and orig_a0 */
> +				if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
> +					perr_and_exit("failed to get tracee registers");
> +				if (ptrace(PTRACE_GETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
> +					perr_and_exit("failed to get tracee registers");
> +
> +				/* Modify a0/orig_a0 for the syscall */
> +				switch (opt) {
> +				case A0_MODIFY:
> +					regs.a0 = A0_NEW;
> +					break;
> +				case ORIG_A0_MODIFY:
> +					orig_a0 = A0_NEW;
> +					break;
> +				}
> +
> +				if (ptrace(PTRACE_SETREGSET, pid, NT_PRSTATUS, &iov))
> +					perr_and_exit("failed to set tracee registers");
> +				if (ptrace(PTRACE_SETREGSET, pid, NT_RISCV_ORIG_A0, &a0_iov))
> +					perr_and_exit("failed to set tracee registers");
> +				switch (i) {
> +				case 1:
> +					/* Stop at the beginning of syscall */
> +					rc = ptrace(PTRACE_GET_SYSCALL_INFO, pid,
> +						sizeof(syscall_info), &syscall_info);
> +					if (rc < 0)
> +						perr_and_exit("failed to get syscall info of entry");
> +					if (rc < expected_sci_entry_size
> +						|| syscall_info.op != PTRACE_SYSCALL_INFO_ENTRY)
> +						perr_and_exit("stop position of entry mismatched");
> +					result[0].orig_a0 = syscall_info.entry.args[0];
> +					break;
> +
> +				case 2:
> +					/* Stop at the end of syscall */
> +					rc = ptrace(PTRACE_GET_SYSCALL_INFO, pid,
> +						sizeof(syscall_info), &syscall_info);
> +					if (rc < 0)
> +						perr_and_exit("failed to get syscall info of entry");
> +					if (rc < expected_sci_exit_size
> +						|| syscall_info.op != PTRACE_SYSCALL_INFO_EXIT)
> +						perr_and_exit("stop position of exit mismatched");
> +					result[0].a0 = syscall_info.exit.rval;
> +
> +					if (ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov))
> +						perr_and_exit("failed to get tracee registers");
> +					result[1].a0 = regs.a0;
> +					if (ptrace(PTRACE_GETREGSET, pid, NT_RISCV_ORIG_A0,
> +						   &a0_iov))
> +						perr_and_exit("failed to get tracee registers");
> +					result[1].orig_a0 = orig_a0;
> +				}
> +			}
> +			if (ptrace(PTRACE_SYSCALL, pid, 0, 0) < 0)
> +				perr_and_exit("failed to resume tracee");
> +		}
> +	}
> +
> +	/* Resume the tracee */
> +	ptrace(PTRACE_CONT, pid, 0, 0);
> +	if (waitpid(pid, &status, 0) != pid)
> +		perr_and_exit("failed to wait for the tracee");
> +
> +}
> +
> +TEST(ptrace_access_a0)
> +{
> +	struct a0_regs result[2];
> +
> +	ptrace_test(A0_MODIFY, result);
> +
> +	/* Verify PTRACE_SETREGSET */
> +	/* The modification of a0 cannot affect the first argument of the syscall */
> +	EXPECT_EQ(A0_OLD, result[0].orig_a0);
> +	EXPECT_EQ(A0_NEW, result[0].a0);
> +
> +	/* Verify PTRACE_GETREGSET */
> +	EXPECT_EQ(result[1].orig_a0, result[0].orig_a0);
> +	EXPECT_EQ(result[1].a0, result[0].a0);
> +}
> +
> +TEST(ptrace_access_orig_a0)
> +{
> +	struct a0_regs result[2];
> +
> +	ptrace_test(ORIG_A0_MODIFY, result);
> +
> +	/* Verify PTRACE_SETREGSET */
> +	/* Only modify orig_a0 to change the first argument of the syscall */
> +	EXPECT_EQ(A0_NEW, result[0].orig_a0);
> +	/* a0 will not be affected */
> +	EXPECT_NE(A0_NEW, result[0].a0);
> +
> +	/* Verify PTRACE_GETREGSET */
> +	EXPECT_EQ(result[1].orig_a0, result[0].orig_a0);
> +	EXPECT_EQ(result[1].a0, result[0].a0);
> +}
> +
> +TEST_HARNESS_MAIN
> 
> -- 
> 2.48.0
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Re: [PATCH v6 1/3] riscv/ptrace: add new regset to access original a0 register

[Charlie Jenkins]

On Wed, Jan 15, 2025 at 07:13:27PM +0800, Celeste Liu wrote:
> The orig_a0 is missing in struct user_regs_struct of riscv, and there is
> no way to add it without breaking UAPI. (See Link tag below)
> 
> Like NT_ARM_SYSTEM_CALL do, we add a new regset name NT_RISCV_ORIG_A0 to
> access original a0 register from userspace via ptrace API.
> 
> Fixes: e2c0cdfba7f6 ("RISC-V: User-facing API")
> Link: https://lore.kernel.org/all/59505464-c84a-403d-972f-d4b2055eeaac@gmail.com/
> Cc: stable@vger.kernel.org
> Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>

Thank you!

Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>

> ---
>  arch/riscv/kernel/ptrace.c | 32 ++++++++++++++++++++++++++++++++
>  include/uapi/linux/elf.h   |  1 +
>  2 files changed, 33 insertions(+)
> 
> diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
> index ea67e9fb7a583683b922fe2c017ea61f3bc848db..ef9ab74c8575a5c440155973b1c625c06a867c97 100644
> --- a/arch/riscv/kernel/ptrace.c
> +++ b/arch/riscv/kernel/ptrace.c
> @@ -31,6 +31,7 @@ enum riscv_regset {
>  #ifdef CONFIG_RISCV_ISA_SUPM
>  	REGSET_TAGGED_ADDR_CTRL,
>  #endif
> +	REGSET_ORIG_A0,
>  };
>  
>  static int riscv_gpr_get(struct task_struct *target,
> @@ -184,6 +185,29 @@ static int tagged_addr_ctrl_set(struct task_struct *target,
>  }
>  #endif
>  
> +static int riscv_orig_a0_get(struct task_struct *target,
> +			     const struct user_regset *regset,
> +			     struct membuf to)
> +{
> +	return membuf_store(&to, task_pt_regs(target)->orig_a0);
> +}
> +
> +static int riscv_orig_a0_set(struct task_struct *target,
> +			     const struct user_regset *regset,
> +			     unsigned int pos, unsigned int count,
> +			     const void *kbuf, const void __user *ubuf)
> +{
> +	unsigned long orig_a0 = task_pt_regs(target)->orig_a0;
> +	int ret;
> +
> +	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &orig_a0, 0, -1);
> +	if (ret)
> +		return ret;
> +
> +	task_pt_regs(target)->orig_a0 = orig_a0;
> +	return 0;
> +}
> +
>  static const struct user_regset riscv_user_regset[] = {
>  	[REGSET_X] = {
>  		.core_note_type = NT_PRSTATUS,
> @@ -224,6 +248,14 @@ static const struct user_regset riscv_user_regset[] = {
>  		.set = tagged_addr_ctrl_set,
>  	},
>  #endif
> +	[REGSET_ORIG_A0] = {
> +		.core_note_type = NT_RISCV_ORIG_A0,
> +		.n = 1,
> +		.size = sizeof(elf_greg_t),
> +		.align = sizeof(elf_greg_t),
> +		.regset_get = riscv_orig_a0_get,
> +		.set = riscv_orig_a0_set,
> +	},
>  };
>  
>  static const struct user_regset_view riscv_user_native_view = {
> diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
> index b44069d29cecc0f9de90ee66bfffd2137f4275a8..390060229601631da2fb27030d9fa2142e676c14 100644
> --- a/include/uapi/linux/elf.h
> +++ b/include/uapi/linux/elf.h
> @@ -452,6 +452,7 @@ typedef struct elf64_shdr {
>  #define NT_RISCV_CSR	0x900		/* RISC-V Control and Status Registers */
>  #define NT_RISCV_VECTOR	0x901		/* RISC-V vector registers */
>  #define NT_RISCV_TAGGED_ADDR_CTRL 0x902	/* RISC-V tagged address control (prctl()) */
> +#define NT_RISCV_ORIG_A0	  0x903	/* RISC-V original a0 register */
>  #define NT_LOONGARCH_CPUCFG	0xa00	/* LoongArch CPU config registers */
>  #define NT_LOONGARCH_CSR	0xa01	/* LoongArch control and status registers */
>  #define NT_LOONGARCH_LSX	0xa02	/* LoongArch Loongson SIMD Extension registers */
> 
> -- 
> 2.48.0
> 

Re: [PATCH v6 2/3] tools: copy include/linux/stddef.h to tools/include

[Charlie Jenkins]

On Wed, Jan 15, 2025 at 07:13:28PM +0800, Celeste Liu wrote:
> Some macro defined in stddef.h are useful and have been used in many
> code in selftests. Copy them to tools/include so developers needn't
> create their copy in every files.
> 
> Remove some definitions like NULL and true/false to be suitable to
> non-kernel environment.
> 
> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>

Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>

> ---
>  tools/include/linux/stddef.h      | 85 +++++++++++++++++++++++++++++++++++++++
>  tools/include/uapi/linux/stddef.h |  6 +--
>  2 files changed, 87 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/include/linux/stddef.h b/tools/include/linux/stddef.h
> new file mode 100644
> index 0000000000000000000000000000000000000000..55f3964d9a3d9f9f9345a75248eec027c56faef9
> --- /dev/null
> +++ b/tools/include/linux/stddef.h
> @@ -0,0 +1,85 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_STDDEF_H
> +#define _LINUX_STDDEF_H
> +
> +#include <uapi/linux/stddef.h>
> +
> +/**
> + * sizeof_field() - Report the size of a struct field in bytes
> + *
> + * @TYPE: The structure containing the field of interest
> + * @MEMBER: The field to return the size of
> + */
> +#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
> +
> +/**
> + * offsetofend() - Report the offset of a struct field within the struct
> + *
> + * @TYPE: The type of the structure
> + * @MEMBER: The member within the structure to get the end offset of
> + */
> +#define offsetofend(TYPE, MEMBER) \
> +	(offsetof(TYPE, MEMBER)	+ sizeof_field(TYPE, MEMBER))
> +
> +/**
> + * struct_group() - Wrap a set of declarations in a mirrored struct
> + *
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical
> + * layout and size: one anonymous and one named. The former can be
> + * used normally without sub-struct naming, and the latter can be
> + * used to reason about the start, end, and size of the group of
> + * struct members.
> + */
> +#define struct_group(NAME, MEMBERS...)	\
> +	__struct_group(/* no tag */, NAME, /* no attrs */, MEMBERS)
> +
> +/**
> + * struct_group_attr() - Create a struct_group() with trailing attributes
> + *
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @ATTRS: Any struct attributes to apply
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical
> + * layout and size: one anonymous and one named. The former can be
> + * used normally without sub-struct naming, and the latter can be
> + * used to reason about the start, end, and size of the group of
> + * struct members. Includes structure attributes argument.
> + */
> +#define struct_group_attr(NAME, ATTRS, MEMBERS...) \
> +	__struct_group(/* no tag */, NAME, ATTRS, MEMBERS)
> +
> +/**
> + * struct_group_tagged() - Create a struct_group with a reusable tag
> + *
> + * @TAG: The tag name for the named sub-struct
> + * @NAME: The identifier name of the mirrored sub-struct
> + * @MEMBERS: The member declarations for the mirrored structs
> + *
> + * Used to create an anonymous union of two structs with identical
> + * layout and size: one anonymous and one named. The former can be
> + * used normally without sub-struct naming, and the latter can be
> + * used to reason about the start, end, and size of the group of
> + * struct members. Includes struct tag argument for the named copy,
> + * so the specified layout can be reused later.
> + */
> +#define struct_group_tagged(TAG, NAME, MEMBERS...) \
> +	__struct_group(TAG, NAME, /* no attrs */, MEMBERS)
> +
> +/**
> + * DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
> + *
> + * @TYPE: The type of each flexible array element
> + * @NAME: The name of the flexible array member
> + *
> + * In order to have a flexible array member in a union or alone in a
> + * struct, it needs to be wrapped in an anonymous struct with at least 1
> + * named member, but that member can be empty.
> + */
> +#define DECLARE_FLEX_ARRAY(TYPE, NAME) \
> +	__DECLARE_FLEX_ARRAY(TYPE, NAME)
> +
> +#endif
> diff --git a/tools/include/uapi/linux/stddef.h b/tools/include/uapi/linux/stddef.h
> index bb6ea517efb51177a7983fadad9b590b12b786e5..f2548fd95f6e1d8cb218d52918bb81a3317d10b1 100644
> --- a/tools/include/uapi/linux/stddef.h
> +++ b/tools/include/uapi/linux/stddef.h
> @@ -1,8 +1,6 @@
>  /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> -#ifndef _LINUX_STDDEF_H
> -#define _LINUX_STDDEF_H
> -
> -
> +#ifndef _UAPI_LINUX_STDDEF_H
> +#define _UAPI_LINUX_STDDEF_H
>  
>  #ifndef __always_inline
>  #define __always_inline __inline__
> 
> -- 
> 2.48.0
> 

Re: [PATCH v6 0/3] riscv/ptrace: add new regset to access original a0 register

[Charlie Jenkins]

On Wed, Jan 15, 2025 at 07:13:26PM +0800, Celeste Liu wrote:
> The orig_a0 is missing in struct user_regs_struct of riscv, and there is
> no way to add it without breaking UAPI. (See Link tag below)
> 
> Like NT_ARM_SYSTEM_CALL do, we add a new regset name NT_RISCV_ORIG_A0 to
> access original a0 register from userspace via ptrace API.
> 
> Link: https://lore.kernel.org/all/59505464-c84a-403d-972f-d4b2055eeaac@gmail.com/
> 
> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
> ---
> Changes in v6:
> - Fix obsolute comment.
> - Copy include/linux/stddef.h to tools/include to use offsetofend in
>   selftests.
> - Link to v5: https://lore.kernel.org/r/20250115-riscv-new-regset-v5-0-d0e6ec031a23@coelacanthus.name
> 
> Changes in v5:
> - Fix wrong usage in selftests.
> - Link to v4: https://lore.kernel.org/r/20241226-riscv-new-regset-v4-0-4496a29d0436@coelacanthus.name
> 
> Changes in v4:
> - Fix a copy paste error in selftest. (Forget to commit...)
> - Link to v3: https://lore.kernel.org/r/20241226-riscv-new-regset-v3-0-f5b96465826b@coelacanthus.name
> 
> Changes in v3:
> - Use return 0 directly for readability.
> - Fix test for modify a0.
> - Add Fixes: tag
> - Remove useless Cc: stable.
> - Selftest will check both a0 and orig_a0, but depends on the
>   correctness of PTRACE_GET_SYSCALL_INFO.
> - Link to v2: https://lore.kernel.org/r/20241203-riscv-new-regset-v2-0-d37da8c0cba6@coelacanthus.name
> 
> Changes in v2:
> - Fix integer width.
> - Add selftest.
> - Link to v1: https://lore.kernel.org/r/20241201-riscv-new-regset-v1-1-c83c58abcc7b@coelacanthus.name
> 
> ---
> Celeste Liu (3):
>       riscv/ptrace: add new regset to access original a0 register
>       tools: copy include/linux/stddef.h to tools/include
>       riscv: selftests: Add a ptrace test to verify a0 and orig_a0 access
> 
>  arch/riscv/kernel/ptrace.c                   |  32 +++++
>  include/uapi/linux/elf.h                     |   1 +
>  tools/include/linux/stddef.h                 |  85 ++++++++++++
>  tools/include/uapi/linux/stddef.h            |   6 +-
>  tools/testing/selftests/riscv/abi/.gitignore |   1 +
>  tools/testing/selftests/riscv/abi/Makefile   |   6 +-
>  tools/testing/selftests/riscv/abi/ptrace.c   | 193 +++++++++++++++++++++++++++
>  7 files changed, 319 insertions(+), 5 deletions(-)
> ---
> base-commit: 0e287d31b62bb53ad81d5e59778384a40f8b6f56
> change-id: 20241201-riscv-new-regset-d529b952ad0d
> 
> Best regards,
> -- 
> Celeste Liu <uwu@coelacanthus.name>
> 

There is also this series that looks like it will solve this problem by
providing an architecture agnostic way of changing syscall args with
PTRACE_SET_SYSCALL_INFO [1].

- Charlie

[1] https://lore.kernel.org/lkml/20250113170925.GA392@altlinux.org/