Commit 18d609da authored by Sidhartha Kumar's avatar Sidhartha Kumar Committed by Linus Torvalds
Browse files

selftest/vm: verify remap destination address in mremap_test 

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.

Link: https://lkml.kernel.org/r/20220420215721.4868-2-sidhartha.kumar@oracle.com


Signed-off-by: default avatarSidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: default avatarShuah Khan <skhan@linuxfoundation.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 9c85a9ba

tools/testing/selftests/vm/mremap_test.c

+39 −3
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <string.h>

#include <sys/mman.h>

#include <time.h>

#include <stdbool.h>



#include "../kselftest.h"
@@ -64,6 +65,30 @@ 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)

{
@@ -179,6 +204,17 @@ 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);