KVM: guest_memfd: MMAP and related fixes

[PATCH v2 13/13] KVM: selftests: Verify that reads to inaccessible guest_memfd VMAs SIGBUS

Posted by Sean Christopherson 2 months, 2 weeks ago

Expand the guest_memfd negative testcases for overflow and MAP_PRIVATE to
verify that reads to inaccessible memory also get a SIGBUS.

Opportunistically fix the write path to use the "val" instead of hardcoding
the literal value a second time, and to use TEST_FAIL(...) instead of
TEST_ASSERT(false, ...).

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/guest_memfd_test.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
index f5372fdf096d..e7d9aeb418d3 100644
--- a/tools/testing/selftests/kvm/guest_memfd_test.c
+++ b/tools/testing/selftests/kvm/guest_memfd_test.c
@@ -84,6 +84,7 @@ static void test_fault_sigbus(int fd, size_t accessible_size, size_t map_size)
 	mem = kvm_mmap(map_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd);
 
 	TEST_EXPECT_SIGBUS(memset(mem, val, map_size));
+	TEST_EXPECT_SIGBUS((void)READ_ONCE(mem[accessible_size]));
 
 	for (i = 0; i < accessible_size; i++)
 		TEST_ASSERT_EQ(READ_ONCE(mem[i]), val);
-- 
2.51.0.618.g983fd99d29-goog

Re: [PATCH v2 13/13] KVM: selftests: Verify that reads to inaccessible guest_memfd VMAs SIGBUS

Posted by Lisa Wang 2 months, 1 week ago

Sean Christopherson <seanjc@google.com> writes:

> Expand the guest_memfd negative testcases for overflow and MAP_PRIVATE to
> verify that reads to inaccessible memory also get a SIGBUS.
>
> Opportunistically fix the write path to use the "val" instead of hardcoding
> the literal value a second time, and to use TEST_FAIL(...) instead of
> TEST_ASSERT(false, ...).
>

Reviewed-by: Lisa Wang <wyihan@google.com>
Tested-by: Lisa Wang <wyihan@google.com>

> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  tools/testing/selftests/kvm/guest_memfd_test.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index f5372fdf096d..e7d9aeb418d3 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -84,6 +84,7 @@ static void test_fault_sigbus(int fd, size_t accessible_size, size_t map_size)
>  	mem = kvm_mmap(map_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd);
>  
>  	TEST_EXPECT_SIGBUS(memset(mem, val, map_size));
> +	TEST_EXPECT_SIGBUS((void)READ_ONCE(mem[accessible_size]));
>  
>  	for (i = 0; i < accessible_size; i++)
>  		TEST_ASSERT_EQ(READ_ONCE(mem[i]), val);
> -- 
> 2.51.0.618.g983fd99d29-goog

Re: [PATCH v2 13/13] KVM: selftests: Verify that reads to inaccessible guest_memfd VMAs SIGBUS

Posted by Ackerley Tng 2 months, 1 week ago

Sean Christopherson <seanjc@google.com> writes:

> Expand the guest_memfd negative testcases for overflow and MAP_PRIVATE to
> verify that reads to inaccessible memory also get a SIGBUS.
>
> Opportunistically fix the write path to use the "val" instead of hardcoding
> the literal value a second time, and to use TEST_FAIL(...) instead of
> TEST_ASSERT(false, ...).
>

The change the use "val" isn't in this patch, and I think the
TEST_FAIL() change was intended for another earlier patch.

Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Tested-by: Ackerley Tng <ackerleytng@google.com>

> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  tools/testing/selftests/kvm/guest_memfd_test.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index f5372fdf096d..e7d9aeb418d3 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -84,6 +84,7 @@ static void test_fault_sigbus(int fd, size_t accessible_size, size_t map_size)
>  	mem = kvm_mmap(map_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd);
>  
>  	TEST_EXPECT_SIGBUS(memset(mem, val, map_size));
> +	TEST_EXPECT_SIGBUS((void)READ_ONCE(mem[accessible_size]));
>  
>  	for (i = 0; i < accessible_size; i++)
>  		TEST_ASSERT_EQ(READ_ONCE(mem[i]), val);
> -- 
> 2.51.0.618.g983fd99d29-goog

Re: [PATCH v2 13/13] KVM: selftests: Verify that reads to inaccessible guest_memfd VMAs SIGBUS

Posted by Sean Christopherson 2 months, 1 week ago

On Mon, Oct 06, 2025, Ackerley Tng wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
> > Expand the guest_memfd negative testcases for overflow and MAP_PRIVATE to
> > verify that reads to inaccessible memory also get a SIGBUS.
> >
> > Opportunistically fix the write path to use the "val" instead of hardcoding
> > the literal value a second time, and to use TEST_FAIL(...) instead of
> > TEST_ASSERT(false, ...).
> >
> 
> The change the use "val" isn't in this patch, and I think the
> TEST_FAIL() change was intended for another earlier patch.

Yep.  I originally had the TEST_ASSERT => TEST_FAIL change in this patch, and
forgot all about the changelog when I added the SIGBUS "catch".

Thanks!