The patch titled
Subject: selftest/vm: verify remap destination address in mremap_test
has been added to the -mm tree. Its filename is
selftest-vm-verify-remap-destination-address-in-mremap_test.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/selftest-vm-verify-remap-destination-address-in-mremap_test.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/selftest-vm-verify-remap-destination-address-in-mremap_test.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Subject: selftest/vm: verify remap destination address in mremap_test
Because mremap does not have a NOREPLACE flag, it can destroy existing
mappings. This can cause a segfault if regions such as text are
destroyed. Verify the requested mremap destination address does not
overlap any existing mappings by using mmap's FIXED_NOREPLACE flag and
checking for the EEXIST error code. Keep incrementing the destination
address until a valid mapping is found or max address is reached.
Link: https://lkml.kernel.org/r/20220414171529.62058-3-sidhartha.kumar@xxxxxxxxxx
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/tools/testing/selftests/vm/mremap_test.c~selftest-vm-verify-remap-destination-address-in-mremap_test
+++ a/tools/testing/selftests/vm/mremap_test.c
@@ -10,6 +10,7 @@
#include <string.h>
#include <sys/mman.h>
#include <time.h>
+#include <limits.h>
#include "../kselftest.h"
@@ -64,6 +65,34 @@ enum {
.expect_failure = should_fail \
}
+/*
+ * Returns 0 if the requested remap region overlaps with an
+ * existing mapping (e.g text, stack) else returns 1.
+ */
+static int remap_region_valid(void *addr, unsigned long long size)
+{
+ void *remap_addr = NULL;
+ int ret = 1;
+
+ if ((unsigned long long) addr > ULLONG_MAX - size) {
+ ksft_print_msg("Can't find a valid region to remap to\n");
+ exit(KSFT_SKIP);
+ }
+
+ /* 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 = 0;
+ } else {
+ munmap(remap_addr, size);
+ }
+
+ return ret;
+}
+
/* Returns mmap_min_addr sysctl */
static unsigned long long get_mmap_min_addr(void)
{
@@ -179,6 +208,13 @@ static long long remap_region(struct con
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 (!remap_region_valid(addr, c.region_size)) {
+ if (c.overlapping)
+ break;
+ addr += c.src_alignment;
+ }
+
clock_gettime(CLOCK_MONOTONIC, &t_start);
dest_addr = mremap(src_addr, c.region_size, c.region_size,
MREMAP_MAYMOVE|MREMAP_FIXED, (char *) addr);
_
Patches currently in -mm which might be from sidhartha.kumar@xxxxxxxxxx are
selftest-vm-verify-mmap-addr-in-mremap_test.patch
selftest-vm-verify-remap-destination-address-in-mremap_test.patch
selftest-vm-support-xfail-in-mremap_test.patch
selftest-vm-add-skip-support-to-mremap_test.patch
selftest-vm-clarify-error-statement-in-gup_test.patch
