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;
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) {
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.
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.
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);
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 "-----------------"
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
linux-kselftest-mirror@lists.linaro.org
-
Andrew Morton -
Shuah Khan -
Sidhartha Kumar