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

On 4/14/22 11:15 AM, Sidhartha Kumar wrote:

Avoid calling mmap with requested addresses that are less than the system's mmap_min_addr. Running the test as root returns EACCES when trying to map addresses < mmap_min_addr which is not one of the error codes for the retry condition. Add a munmap call after an alignment check as the mappings are retained after the retry and can reach vm.max_map_count.

Please use 75 or 76 chars per line in change logs to make it easier to read the commit log.

The description is a bit confusing. What happens when mmap tries to map addresses < mmap_min_addr?

Signed-off-by: Sidhartha Kumar sidhartha.kumar@oracle.com

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..58600fee4b81 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 */

Change this to "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;
  

Should this be an error or retry? Can you add why this is a retry when addr < mmap_min_addr?

• 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;

thanks, -- Shuah