[PATCH v2 1/4] selftest/vm: verify mmap addr in mremap_test

[PATCH v2 1/4] selftest/vm: verify mmap addr in mremap_test

[Sidhartha Kumar]

Avoid calling mmap with requested addresses that are less than the system's
mmap_min_addr. When run as root, mmap returns EACCES when trying to map
addresses < mmap_min_addr. This is not one of the error codes for the
condition to retry the mmap in the test. Rather than arbitrarily retrying
on EACCES, don't attempt an mmap until addr > vm.mmap_min_addr. 

Add a munmap call after an alignment check as the mappings are retained
after the retry and can reach the vm.max_map_count sysctl.

Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
---
v2:
-change comment for description of get_mmap_min_addr()
-fix commit message formatting

 tools/testing/selftests/vm/mremap_test.c | 41 +++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vm/mremap_test.c b/tools/testing/selftests/vm/mremap_test.c
index 0624d1bd71b5..2b3b4f15185f 100644
--- a/tools/testing/selftests/vm/mremap_test.c
+++ b/tools/testing/selftests/vm/mremap_test.c
@@ -6,6 +6,7 @@
 
 #include <errno.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
 #include <sys/mman.h>
 #include <time.h>
@@ -64,6 +65,35 @@ enum {
 	.expect_failure = should_fail				\
 }
 
+/* Returns mmap_min_addr sysctl tunable from procfs */
+static unsigned long long get_mmap_min_addr(void)
+{
+	FILE *fp;
+	int n_matched;
+	static unsigned long long addr;
+
+	if (addr)
+		return addr;
+
+	fp = fopen("/proc/sys/vm/mmap_min_addr", "r");
+	if (fp == NULL) {
+		ksft_print_msg("Failed to open /proc/sys/vm/mmap_min_addr: %s\n",
+			strerror(errno));
+		exit(KSFT_SKIP);
+	}
+
+	n_matched = fscanf(fp, "%llu", &addr);
+	if (n_matched != 1) {
+		ksft_print_msg("Failed to read /proc/sys/vm/mmap_min_addr: %s\n",
+			strerror(errno));
+		fclose(fp);
+		exit(KSFT_SKIP);
+	}
+
+	fclose(fp);
+	return addr;
+}
+
 /*
  * Returns the start address of the mapping on success, else returns
  * NULL on failure.
@@ -72,8 +102,15 @@ static void *get_source_mapping(struct config c)
 {
 	unsigned long long addr = 0ULL;
 	void *src_addr = NULL;
+	unsigned long long mmap_min_addr;
+
+	mmap_min_addr = get_mmap_min_addr();
+
 retry:
 	addr += c.src_alignment;
+	if (addr < mmap_min_addr)
+		goto retry;
+
 	src_addr = mmap((void *) addr, c.region_size, PROT_READ | PROT_WRITE,
 			MAP_FIXED_NOREPLACE | MAP_ANONYMOUS | MAP_SHARED,
 			-1, 0);
@@ -91,8 +128,10 @@ static void *get_source_mapping(struct config c)
 	 * alignment in the tests.
 	 */
 	if (((unsigned long long) src_addr & (c.src_alignment - 1)) ||
-			!((unsigned long long) src_addr & c.src_alignment))
+			!((unsigned long long) src_addr & c.src_alignment)) {
+		munmap(src_addr, c.region_size);
 		goto retry;
+	}
 
 	if (!src_addr)
 		goto error;
-- 
2.27.0

[PATCH v2 2/4] selftest/vm: verify remap destination address in mremap_test

[Sidhartha Kumar]

Because mremap does not have a MAP_FIXED_NOREPLACE flag, it can destroy
existing mappings. This causes a segfault when regions such as text are
remapped and the permissions are changed.

Verify the requested mremap destination address does not overlap any
existing mappings by using mmap's MAP_FIXED_NOREPLACE flag. Keep 
incrementing the destination address until a valid mapping is found or
fail the current test once the max address is reached.

Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
---
v2:
-rename remap_region_valid() to is_remap_region_valid().
-change return value of is_remap_region_valid() to bool.
-take out overflow check from is_remap_region_valid() to 
 inside caller.
-fail just the current test on overflow rather than existing 
 the program
-fix alignment of mmap calls
-change "can't" to "couldn't" in error message
-increment mremap destination address by dest_alignment
 rather than src_alignment

 tools/testing/selftests/vm/mremap_test.c | 42 ++++++++++++++++++++++--
 1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/vm/mremap_test.c b/tools/testing/selftests/vm/mremap_test.c
index 2b3b4f15185f..e3ce33a9954e 100644
--- a/tools/testing/selftests/vm/mremap_test.c
+++ b/tools/testing/selftests/vm/mremap_test.c
@@ -10,6 +10,7 @@
 #include <string.h>
 #include <sys/mman.h>
 #include <time.h>
+#include <stdbool.h>
 
 #include "../kselftest.h"
 
@@ -65,6 +66,30 @@ enum {
 	.expect_failure = should_fail				\
 }
 
+/*
+ * Returns false if the requested remap region overlaps with an
+ * existing mapping (e.g text, stack) else returns true.
+ */
+static bool is_remap_region_valid(void *addr, unsigned long long size)
+{
+	void *remap_addr = NULL;
+	bool ret = true;
+
+	/* Use MAP_FIXED_NOREPLACE flag to ensure region is not mapped */
+	remap_addr = mmap(addr, size, PROT_READ | PROT_WRITE,
+					 MAP_FIXED_NOREPLACE | MAP_ANONYMOUS | MAP_SHARED,
+					 -1, 0);
+
+	if (remap_addr == MAP_FAILED) {
+		if (errno == EEXIST)
+			ret = false;
+	} else {
+		munmap(remap_addr, size);
+	}
+
+	return ret;
+}
+
 /* Returns mmap_min_addr sysctl tunable from procfs */
 static unsigned long long get_mmap_min_addr(void)
 {
@@ -112,8 +137,8 @@ static void *get_source_mapping(struct config c)
 		goto retry;
 
 	src_addr = mmap((void *) addr, c.region_size, PROT_READ | PROT_WRITE,
-			MAP_FIXED_NOREPLACE | MAP_ANONYMOUS | MAP_SHARED,
-			-1, 0);
+					MAP_FIXED_NOREPLACE | MAP_ANONYMOUS | MAP_SHARED,
+					-1, 0);
 	if (src_addr == MAP_FAILED) {
 		if (errno == EPERM || errno == EEXIST)
 			goto retry;
@@ -180,9 +205,20 @@ static long long remap_region(struct config c, unsigned int threshold_mb,
 	if (!((unsigned long long) addr & c.dest_alignment))
 		addr = (void *) ((unsigned long long) addr | c.dest_alignment);
 
+	/* Don't destroy existing mappings unless expected to overlap */
+	while (!is_remap_region_valid(addr, c.region_size) && !c.overlapping) {
+		/* Check for unsigned overflow */
+		if (addr + c.dest_alignment < addr) {
+			ksft_print_msg("Couldn't find a valid region to remap to\n");
+			ret = -1;
+			goto out;
+		}
+		addr += c.dest_alignment;
+	}
+
 	clock_gettime(CLOCK_MONOTONIC, &t_start);
 	dest_addr = mremap(src_addr, c.region_size, c.region_size,
-			MREMAP_MAYMOVE|MREMAP_FIXED, (char *) addr);
+					  MREMAP_MAYMOVE|MREMAP_FIXED, (char *) addr);
 	clock_gettime(CLOCK_MONOTONIC, &t_end);
 
 	if (dest_addr == MAP_FAILED) {
-- 
2.27.0

Re: [PATCH v2 2/4] selftest/vm: verify remap destination address in mremap_test

[Shuah Khan]

On 4/20/22 3:57 PM, Sidhartha Kumar wrote:
> Because mremap does not have a MAP_FIXED_NOREPLACE flag, it can destroy
> existing mappings. This causes a segfault when regions such as text are
> remapped and the permissions are changed.
> 
> Verify the requested mremap destination address does not overlap any
> existing mappings by using mmap's MAP_FIXED_NOREPLACE flag. Keep
> incrementing the destination address until a valid mapping is found or
> fail the current test once the max address is reached.
> 
> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> ---
> v2:
> -rename remap_region_valid() to is_remap_region_valid().
> -change return value of is_remap_region_valid() to bool.
> -take out overflow check from is_remap_region_valid() to
>   inside caller.
> -fail just the current test on overflow rather than existing
>   the program
> -fix alignment of mmap calls
> -change "can't" to "couldn't" in error message
> -increment mremap destination address by dest_alignment
>   rather than src_alignment
> 
Thank you.

Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>

Andrew, please let me know if you would like me to take this
through kselftest tree.

Re: [PATCH v2 2/4] selftest/vm: verify remap destination address in mremap_test

[Andrew Morton]

On Thu, 21 Apr 2022 13:31:56 -0600 Shuah Khan <skhan@linuxfoundation.org> wrote:

> Andrew, please let me know if you would like me to take this
> through kselftest tree.

I'm easy.  If it turns up in linux-next via your tree, I drop the -mm copy.

[PATCH v2 3/4] selftest/vm: support xfail in mremap_test

[Sidhartha Kumar]

Use ksft_test_result_xfail for the tests which are expected to fail.

Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
---
v2:
-add Reviewed-by tag
-fix commit message formatting

 tools/testing/selftests/vm/mremap_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vm/mremap_test.c b/tools/testing/selftests/vm/mremap_test.c
index e3ce33a9954e..237b7ccfa333 100644
--- a/tools/testing/selftests/vm/mremap_test.c
+++ b/tools/testing/selftests/vm/mremap_test.c
@@ -269,7 +269,7 @@ static void run_mremap_test_case(struct test test_case, int *failures,
 
 	if (remap_time < 0) {
 		if (test_case.expect_failure)
-			ksft_test_result_pass("%s\n\tExpected mremap failure\n",
+			ksft_test_result_xfail("%s\n\tExpected mremap failure\n",
 					      test_case.name);
 		else {
 			ksft_test_result_fail("%s\n", test_case.name);
-- 
2.27.0

[PATCH v2 4/4] selftest/vm: add skip support to mremap_test

[Sidhartha Kumar]

Allow the mremap test to be skipped due to errors such as failing to parse
the mmap_min_addr sysctl.

Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
---
v2:
-add Reviewed-by tag
-fix commit message formatting

 tools/testing/selftests/vm/run_vmtests.sh | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/vm/run_vmtests.sh b/tools/testing/selftests/vm/run_vmtests.sh
index 88e15fbb5027..eae98f5de2cc 100755
--- a/tools/testing/selftests/vm/run_vmtests.sh
+++ b/tools/testing/selftests/vm/run_vmtests.sh
@@ -272,11 +272,16 @@ echo "-------------------"
 echo "running mremap_test"
 echo "-------------------"
 ./mremap_test
-if [ $? -ne 0 ]; then
+ret_val=$?
+
+if [ $ret_val -eq 0 ]; then
+	echo "[PASS]"
+elif [ $ret_val -eq $ksft_skip ]; then
+	 echo "[SKIP]"
+	 exitcode=$ksft_skip
+else
 	echo "[FAIL]"
 	exitcode=1
-else
-	echo "[PASS]"
 fi
 
 echo "-----------------"
-- 
2.27.0

Re: [PATCH v2 1/4] selftest/vm: verify mmap addr in mremap_test

[Shuah Khan]

On 4/20/22 3:57 PM, Sidhartha Kumar wrote:
> Avoid calling mmap with requested addresses that are less than the system's
> mmap_min_addr. When run as root, mmap returns EACCES when trying to map
> addresses < mmap_min_addr. This is not one of the error codes for the
> condition to retry the mmap in the test. Rather than arbitrarily retrying
> on EACCES, don't attempt an mmap until addr > vm.mmap_min_addr.
> 
> Add a munmap call after an alignment check as the mappings are retained
> after the retry and can reach the vm.max_map_count sysctl.
> 
> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> ---
> v2:
> -change comment for description of get_mmap_min_addr()
> -fix commit message formatting
> 

Thank you.

Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>

Andrew, please let me know if you would like me to take this
through kselftest tree.

thanks,
-- Shuah