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selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()

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Currently, VA exhaustion is being checked by passing a hint to mmap() and
expecting it to fail.

While populating the lower VA space, mmap() fails because we have 
exhausted the space.

Then, in validate_lower_address_hint(), because mmap() fails, we
confirm that we have indeed exhausted the space.  There is a circular
logic involved here.

Assume that there is a bug in mmap(), also assume that it exists
independent of whether you pass a hint address or not; that for some
reason it is not able to find a 1GB chunk.  My idea is to assert the
exhaustion against some other method.

This patch makes a stricter test by successful
write() calls from /proc/self/maps to a dump file, confirming that a free
chunk is indeed not available.

[dev.jain@arm.com: replace SZ_1GB with MAP_CHUNK_SIZE, tidy-up]
  Link: https://lkml.kernel.org/r/20240325042653.867055-1-dev.jain@arm.com
Link: https://lkml.kernel.org/r/20240321103522.516097-1-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Dev Jain 2024-03-21 16:05:22 +05:30 committed by Andrew Morton
parent 42a346b41c
commit 0104096498
1 changed files with 66 additions and 0 deletions
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66
tools/testing/selftests/mm/virtual_address_range.c
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@ -12,6 +12,8 @@
#include <errno.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <fcntl.h>
#include "../kselftest.h"
/*
@ -93,6 +95,66 @@ static int validate_lower_address_hint(void)
return 1;
}
static int validate_complete_va_space(void)
{
unsigned long start_addr, end_addr, prev_end_addr;
char line[400];
char prot[6];
FILE *file;
int fd;
fd = open("va_dump", O_CREAT | O_WRONLY, 0600);
unlink("va_dump");
if (fd < 0) {
ksft_test_result_skip("cannot create or open dump file\n");
ksft_finished();
}
file = fopen("/proc/self/maps", "r");
if (file == NULL)
ksft_exit_fail_msg("cannot open /proc/self/maps\n");
prev_end_addr = 0;
while (fgets(line, sizeof(line), file)) {
unsigned long hop;
if (sscanf(line, "%lx-%lx %s[rwxp-]",
&start_addr, &end_addr, prot) != 3)
ksft_exit_fail_msg("cannot parse /proc/self/maps\n");
/* end of userspace mappings; ignore vsyscall mapping */
if (start_addr & (1UL << 63))
return 0;
/* /proc/self/maps must have gaps less than MAP_CHUNK_SIZE */
if (start_addr - prev_end_addr >= MAP_CHUNK_SIZE)
return 1;
prev_end_addr = end_addr;
if (prot[0] != 'r')
continue;
/*
* Confirm whether MAP_CHUNK_SIZE chunk can be found or not.
* If write succeeds, no need to check MAP_CHUNK_SIZE - 1
* addresses after that. If the address was not held by this
* process, write would fail with errno set to EFAULT.
* Anyways, if write returns anything apart from 1, exit the
* program since that would mean a bug in /proc/self/maps.
*/
hop = 0;
while (start_addr + hop < end_addr) {
if (write(fd, (void *)(start_addr + hop), 1) != 1)
return 1;
lseek(fd, 0, SEEK_SET);
hop += MAP_CHUNK_SIZE;
}
}
return 0;
}
int main(int argc, char *argv[])
{
char *ptr[NR_CHUNKS_LOW];
@ -133,6 +195,10 @@ int main(int argc, char *argv[])
validate_addr(hptr[i], 1);
}
hchunks = i;
if (validate_complete_va_space()) {
ksft_test_result_fail("BUG in mmap() or /proc/self/maps\n");
ksft_finished();
}
for (i = 0; i < lchunks; i++)
munmap(ptr[i], MAP_CHUNK_SIZE);