Re: [igt-dev] [PATCH i-g-t] i915/gem_mmap_gtt: Race mmap offset generation against closure

[Abdiel Janulgue <abdiel.janulgue@linux.intel.com>]

Yup, this is a valid issue.

Reviewed-by: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>

On 26/08/2019 18.20, Chris Wilson wrote:
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
> ---
>  tests/i915/gem_mmap_gtt.c | 98 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 98 insertions(+)
> 
> diff --git a/tests/i915/gem_mmap_gtt.c b/tests/i915/gem_mmap_gtt.c
> index 8eff91850..81068f7d1 100644
> --- a/tests/i915/gem_mmap_gtt.c
> +++ b/tests/i915/gem_mmap_gtt.c
> @@ -26,6 +26,7 @@
>   */
>  
>  #include <unistd.h>
> +#include <stdatomic.h>
>  #include <stdlib.h>
>  #include <stdio.h>
>  #include <string.h>
> @@ -360,6 +361,99 @@ test_isolation(int i915)
>  	igt_assert(ptr == MAP_FAILED);
>  }
>  
> +static void
> +test_close_race(int i915)
> +{
> +	const int ncpus = sysconf(_SC_NPROCESSORS_ONLN);
> +	uint32_t *handles;
> +
> +	handles = mmap64(0, 4096, PROT_WRITE, MAP_SHARED | MAP_ANON, -1, 0);
> +	igt_assert(handles != MAP_FAILED);
> +
> +	igt_fork(child, ncpus) {
> +		do {
> +			struct drm_i915_gem_mmap_gtt mmap_arg = {};
> +			int i = 1 + random() % ncpus;
> +			uint32_t old;
> +
> +			mmap_arg.handle = gem_create(i915, 4096);
> +			old = atomic_exchange(&handles[i], mmap_arg.handle);
> +			ioctl(i915, DRM_IOCTL_GEM_CLOSE, &old);
> +
> +			if (ioctl(i915,
> +				  DRM_IOCTL_I915_GEM_MMAP_GTT,
> +				  &mmap_arg) != -1) {
> +				void *ptr;
> +
> +				ptr = mmap64(0, 4096,
> +					     PROT_READ, MAP_SHARED, i915,
> +					     mmap_arg.offset);
> +				if (ptr != MAP_FAILED)
> +					munmap(ptr, 4096);
> +			}
> +		} while (!READ_ONCE(handles[0]));
> +	}
> +
> +	sleep(20);
> +	handles[0] = 1;
> +	igt_waitchildren();
> +
> +	for (int i = 1; i <= ncpus; i++)
> +		ioctl(i915, DRM_IOCTL_GEM_CLOSE, handles[i]);
> +	munmap(handles, 4096);
> +}
> +
> +static void
> +test_flink_race(int i915)
> +{
> +	const int ncpus = sysconf(_SC_NPROCESSORS_ONLN);
> +	uint32_t *handles;
> +
> +	handles = mmap64(0, 4096, PROT_WRITE, MAP_SHARED | MAP_ANON, -1, 0);
> +	igt_assert(handles != MAP_FAILED);
> +
> +	igt_fork(child, ncpus) {
> +		int fd = gem_reopen_driver(i915);
> +
> +		do {
> +			struct drm_i915_gem_mmap_gtt mmap_arg = {};
> +			uint32_t old;
> +			int i = 1 + random() % ncpus;
> +
> +			old = atomic_exchange(&handles[i],
> +					      gem_create(i915, 4096));
> +			if (!old)
> +				continue;
> +
> +			mmap_arg.handle =
> +				gem_open(fd, gem_flink(i915, old));
> +			ioctl(i915, DRM_IOCTL_GEM_CLOSE, &old);
> +
> +			if (ioctl(fd,
> +				  DRM_IOCTL_I915_GEM_MMAP_GTT,
> +				  &mmap_arg) != -1) {
> +				void *ptr;
> +
> +				ptr = mmap64(0, 4096,
> +					     PROT_READ, MAP_SHARED, fd,
> +					     mmap_arg.offset);
> +				if (ptr != MAP_FAILED)
> +					munmap(ptr, 4096);
> +			}
> +
> +			ioctl(fd, DRM_IOCTL_GEM_CLOSE, &mmap_arg.handle);
> +		} while (!READ_ONCE(handles[0]));
> +	}
> +
> +	sleep(20);
> +	handles[0] = 1;
> +	igt_waitchildren();
> +
> +	for (int i = 1; i <= ncpus; i++)
> +		ioctl(i915, DRM_IOCTL_GEM_CLOSE, handles[i]);
> +	munmap(handles, 4096);
> +}
> +
>  static void
>  test_write_gtt(int fd)
>  {
> @@ -985,6 +1079,10 @@ igt_main
>  		test_wc(fd);
>  	igt_subtest("isolation")
>  		test_isolation(fd);
> +	igt_subtest("close-race")
> +		test_close_race(fd);
> +	igt_subtest("flink-race")
> +		test_flink_race(fd);
>  	igt_subtest("pf-nonblock")
>  		test_pf_nonblock(fd);
>  
> 
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