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Peter Anvin" To: "H. Peter Anvin" , "Jason A. Donenfeld" , "Peter Zijlstra (Intel)" , "Theodore Ts'o" , =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= , Xin Li , Andrew Cooper , Andy Lutomirski , Ard Biesheuvel , Borislav Petkov , Brian Gerst , Dave Hansen , Ingo Molnar , James Morse , Jarkko Sakkinen , Josh Poimboeuf , Kees Cook , Nam Cao , Oleg Nesterov , Perry Yuan , Thomas Gleixner , Thomas Huth , Uros Bizjak , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-sgx@vger.kernel.org, x86@kernel.org Subject: [PATCH v4 10/10] x86/entry/vdso32: when using int $0x80, use it directly Date: Tue, 16 Dec 2025 13:26:04 -0800 Message-ID: <20251216212606.1325678-11-hpa@zytor.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251216212606.1325678-1-hpa@zytor.com> References: <20251216212606.1325678-1-hpa@zytor.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 0E7B58000E X-Rspamd-Server: rspam04 X-Stat-Signature: uudz4kwt3i5kh646tdn9gjzuwnpztzb5 X-HE-Tag: 1765920416-821755 X-HE-Meta: U2FsdGVkX18I0zIdKGe4L72f14ftOfXOcqMAoNC9jX9PRlM9MjYn/cI2CvfDjv1EDOSQjSs6FWnnkYOlQk+MNCuo3yAISo30tXWvT4f0JAEtRr/1i4XtZMLYlqq6JzBM7m0Fs1IRtgH4VEpWREtn8LA51wjLzUAJCprfTkBrYboUhetV/XWGzgvoKYjpwDtVGhXIUwmtegkOx3p6Mc3Axq78PfyKKtxvQOzMIvYqMGgcuMlNGUZmc0Mm07W7AG6fw8bZ6eX4xbdMYlNZ6CqFYOxuWIqjziePssCw1dcVFobefNILBZU83BPwpOjw5OGiJ0uxJ8RudgybaJiCwl1yEHcAy/eZ4DZM2MmJONAwnszarLGz1+/wxWTkx0Imo0F1aEhQgfb7FrUFpEDFVB5E8l1G9J7PZBXiXN6FkU+OMXDHAOGmX4l4yszySiGnR7b/FTALMd8Pc4nhJ9UuECXXCeE7clssvbfv0i9Fkeg6BDE+5Yf2VVRr/654t3KgrY36usvv2kEs+EYbDnfsMk/b5WGA3P90LGD6ovXCs7kyX0AIrQUa6D2rxW/SP9Md/IbfnpP4lr25wkDqwXt9QaxXG4qzeA/DSCmmsj7SdniXvgtKoPCokWL+hS44GgAl/C8ksqm/3sKGJblHC0xehTUE61QD99/ykUphiyaxJgViGqytp0I8chsVYkrLJn0lOzYhzriBPijkoW7j6VERGN8bc2jG25PN8o7otzqAhiTeH4UuzPY7Oeg2uaVJAfi/DVnScfbtMDHzYlK89Io8j+3LuIa1BBrfabeyTUE2lWM4M12Xy7o4fc5xC6usQNeiKB85nn1RbeZjweGQTUXBcjAM4tXDq2gimmj0gqF/dyJrESy1M81/mvUtmxRViz8gVJzcF5O16lkLCZSe9/dYFfM+8U71XXoZ4cnDF85luTih9ZOETXJEUBMUcJpqpXUCdFd3qD5kz3mtdWYF7GmKHEl jC8Gf5t6 gf4TKov5SXpVDJMyMccoWiIxZfCZgtEVKyrJlSe7JOt8KSnthYIg/s/jAzkfdq8HudH3B1EfmFlxoCJ/UhZthNlEoz/VumfuHskLMw2tWYDU5chQ93K8JgDL3c2aXdJMpjEbOnvxqovbFfU+VJyYdyIcrHzdMWY/5NEEucJ38K+kEPCFDK4rkklOixy7B05pLdvStSnFxpNCzveCH9Tp+9ztLqDIwyxkqpfzfQTUoA02vUjfEgi4tP5UJ2SNd4p+gvdno3sGx09i0nYauozRoaDOcGlfxgnAZkgK2RPrkGeUbOXlfxeo7NcpHqBeHMh3njLxGQmgq53qJHdKC9gdS5cSi9w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: When neither sysenter32 nor syscall32 is available (on either FRED-capable 64-bit hardware or old 32-bit hardware), there is no reason to do a bunch of stack shuffling in __kernel_vsyscall. Unfortunately, just overwriting the initial "push" instructions will mess up the CFI annotations, so suffer the 3-byte NOP if not applicable. Similarly, inline the int $0x80 when doing inline system calls in the vdso instead of calling __kernel_vsyscall. Signed-off-by: H. Peter Anvin (Intel) --- arch/x86/entry/vdso/vdso32/system_call.S | 18 ++++++++++++++---- arch/x86/include/asm/vdso/sys_call.h | 4 +++- 2 files changed, 17 insertions(+), 5 deletions(-) diff --git a/arch/x86/entry/vdso/vdso32/system_call.S b/arch/x86/entry/vdso/vdso32/system_call.S index 7b1c0f16e511..9157cf9c5749 100644 --- a/arch/x86/entry/vdso/vdso32/system_call.S +++ b/arch/x86/entry/vdso/vdso32/system_call.S @@ -14,6 +14,18 @@ ALIGN __kernel_vsyscall: CFI_STARTPROC + + /* + * If using int $0x80, there is no reason to muck about with the + * stack here. Unfortunately just overwriting the push instructions + * would mess up the CFI annotations, but it is only a 3-byte + * NOP in that case. This could be avoided by patching the + * vdso symbol table (not the code) and entry point, but that + * would a fair bit of tooling work or by simply compiling + * two different vDSO images, but that doesn't seem worth it. + */ + ALTERNATIVE "int $0x80; ret", "", X86_FEATURE_SYSFAST32 + /* * Reshuffle regs so that all of any of the entry instructions * will preserve enough state. @@ -52,11 +64,9 @@ __kernel_vsyscall: #define SYSENTER_SEQUENCE "movl %esp, %ebp; sysenter" #define SYSCALL_SEQUENCE "movl %ecx, %ebp; syscall" - /* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */ - ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSFAST32, \ - SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32 + ALTERNATIVE SYSENTER_SEQUENCE, SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32 - /* Enter using int $0x80 */ + /* Re-enter using int $0x80 */ int $0x80 SYM_INNER_LABEL(int80_landing_pad, SYM_L_GLOBAL) diff --git a/arch/x86/include/asm/vdso/sys_call.h b/arch/x86/include/asm/vdso/sys_call.h index dcfd17c6dd57..5806b1cd6aef 100644 --- a/arch/x86/include/asm/vdso/sys_call.h +++ b/arch/x86/include/asm/vdso/sys_call.h @@ -20,7 +20,9 @@ # define __sys_reg4 "r10" # define __sys_reg5 "r8" #else -# define __sys_instr "call __kernel_vsyscall" +# define __sys_instr ALTERNATIVE("ds;ds;ds;int $0x80", \ + "call __kernel_vsyscall", \ + X86_FEATURE_SYSFAST32) # define __sys_clobber "memory" # define __sys_nr(x,y) __NR_ ## x ## y # define __sys_reg1 "ebx" -- 2.52.0