[PATCH] KVM: selftests: Fix mapping length truncation in m{,un}map()

[PATCH] KVM: selftests: Fix mapping length truncation in m{,un}map()

[Zenghui Yu]

max_mem_slots is now declared as uint32_t. The result of (0x200000 * 32767)
is unexpectedly truncated to be 0xffe00000, whilst we actually need to
allocate about, 63GB. Cast max_mem_slots to size_t in both mmap() and
munmap() to fix the length truncation.

We'll otherwise see the failure on arm64 thanks to the access_ok() checking
in __kvm_set_memory_region(), as the unmapped VA happen to go beyond the
task's allowed address space.

 # ./set_memory_region_test
Allowed number of memory slots: 32767
Adding slots 0..32766, each memory region with 2048K size
==== Test Assertion Failure ====
  set_memory_region_test.c:391: ret == 0
  pid=94861 tid=94861 errno=22 - Invalid argument
     1	0x00000000004015a7: test_add_max_memory_regions at set_memory_region_test.c:389
     2	 (inlined by) main at set_memory_region_test.c:426
     3	0x0000ffffb8e67bdf: ?? ??:0
     4	0x00000000004016db: _start at :?
  KVM_SET_USER_MEMORY_REGION IOCTL failed,
  rc: -1 errno: 22 slot: 2615

Fixes: 3bf0fcd75434 ("KVM: selftests: Speed up set_memory_region_test")
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
---
 tools/testing/selftests/kvm/set_memory_region_test.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
index d79d58eada9f..85b18bb8f762 100644
--- a/tools/testing/selftests/kvm/set_memory_region_test.c
+++ b/tools/testing/selftests/kvm/set_memory_region_test.c
@@ -376,7 +376,7 @@ static void test_add_max_memory_regions(void)
 	pr_info("Adding slots 0..%i, each memory region with %dK size\n",
 		(max_mem_slots - 1), MEM_REGION_SIZE >> 10);
 
-	mem = mmap(NULL, MEM_REGION_SIZE * max_mem_slots + alignment,
+	mem = mmap(NULL, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment,
 		   PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 	TEST_ASSERT(mem != MAP_FAILED, "Failed to mmap() host");
 	mem_aligned = (void *)(((size_t) mem + alignment - 1) & ~(alignment - 1));
@@ -401,7 +401,7 @@ static void test_add_max_memory_regions(void)
 	TEST_ASSERT(ret == -1 && errno == EINVAL,
 		    "Adding one more memory slot should fail with EINVAL");
 
-	munmap(mem, MEM_REGION_SIZE * max_mem_slots + alignment);
+	munmap(mem, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment);
 	munmap(mem_extra, MEM_REGION_SIZE);
 	kvm_vm_free(vm);
 }
-- 
2.19.1

Re: [PATCH] KVM: selftests: Fix mapping length truncation in m{,un}map()

[Paolo Bonzini]

On 24/06/21 09:09, Zenghui Yu wrote:
> max_mem_slots is now declared as uint32_t. The result of (0x200000 * 32767)
> is unexpectedly truncated to be 0xffe00000, whilst we actually need to
> allocate about, 63GB. Cast max_mem_slots to size_t in both mmap() and
> munmap() to fix the length truncation.
> 
> We'll otherwise see the failure on arm64 thanks to the access_ok() checking
> in __kvm_set_memory_region(), as the unmapped VA happen to go beyond the
> task's allowed address space.
> 
>   # ./set_memory_region_test
> Allowed number of memory slots: 32767
> Adding slots 0..32766, each memory region with 2048K size
> ==== Test Assertion Failure ====
>    set_memory_region_test.c:391: ret == 0
>    pid=94861 tid=94861 errno=22 - Invalid argument
>       1	0x00000000004015a7: test_add_max_memory_regions at set_memory_region_test.c:389
>       2	 (inlined by) main at set_memory_region_test.c:426
>       3	0x0000ffffb8e67bdf: ?? ??:0
>       4	0x00000000004016db: _start at :?
>    KVM_SET_USER_MEMORY_REGION IOCTL failed,
>    rc: -1 errno: 22 slot: 2615
> 
> Fixes: 3bf0fcd75434 ("KVM: selftests: Speed up set_memory_region_test")
> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
> ---
>   tools/testing/selftests/kvm/set_memory_region_test.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
> index d79d58eada9f..85b18bb8f762 100644
> --- a/tools/testing/selftests/kvm/set_memory_region_test.c
> +++ b/tools/testing/selftests/kvm/set_memory_region_test.c
> @@ -376,7 +376,7 @@ static void test_add_max_memory_regions(void)
>   	pr_info("Adding slots 0..%i, each memory region with %dK size\n",
>   		(max_mem_slots - 1), MEM_REGION_SIZE >> 10);
>   
> -	mem = mmap(NULL, MEM_REGION_SIZE * max_mem_slots + alignment,
> +	mem = mmap(NULL, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment,
>   		   PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>   	TEST_ASSERT(mem != MAP_FAILED, "Failed to mmap() host");
>   	mem_aligned = (void *)(((size_t) mem + alignment - 1) & ~(alignment - 1));
> @@ -401,7 +401,7 @@ static void test_add_max_memory_regions(void)
>   	TEST_ASSERT(ret == -1 && errno == EINVAL,
>   		    "Adding one more memory slot should fail with EINVAL");
>   
> -	munmap(mem, MEM_REGION_SIZE * max_mem_slots + alignment);
> +	munmap(mem, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment);
>   	munmap(mem_extra, MEM_REGION_SIZE);
>   	kvm_vm_free(vm);
>   }
> 

Queued, thanks.

Paolo

Re: [PATCH] KVM: selftests: Fix mapping length truncation in m{,un}map()

[Christian Borntraeger]

On 24.06.21 09:09, Zenghui Yu wrote:
> max_mem_slots is now declared as uint32_t. The result of (0x200000 * 32767)
> is unexpectedly truncated to be 0xffe00000, whilst we actually need to
> allocate about, 63GB. Cast max_mem_slots to size_t in both mmap() and
> munmap() to fix the length truncation.
> 
> We'll otherwise see the failure on arm64 thanks to the access_ok() checking
> in __kvm_set_memory_region(), as the unmapped VA happen to go beyond the
> task's allowed address space.
> 
>   # ./set_memory_region_test
> Allowed number of memory slots: 32767
> Adding slots 0..32766, each memory region with 2048K size
> ==== Test Assertion Failure ====
>    set_memory_region_test.c:391: ret == 0
>    pid=94861 tid=94861 errno=22 - Invalid argument
>       1	0x00000000004015a7: test_add_max_memory_regions at set_memory_region_test.c:389
>       2	 (inlined by) main at set_memory_region_test.c:426
>       3	0x0000ffffb8e67bdf: ?? ??:0
>       4	0x00000000004016db: _start at :?
>    KVM_SET_USER_MEMORY_REGION IOCTL failed,
>    rc: -1 errno: 22 slot: 2615
> 
> Fixes: 3bf0fcd75434 ("KVM: selftests: Speed up set_memory_region_test")
> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>

While likely correct, this now breaks on many test systems in our CI that have less memory than 64GB.
(We do get ENOMEM). I have not seen the ENOMEM failures in earlier versions. Strange

> ---
>   tools/testing/selftests/kvm/set_memory_region_test.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
> index d79d58eada9f..85b18bb8f762 100644
> --- a/tools/testing/selftests/kvm/set_memory_region_test.c
> +++ b/tools/testing/selftests/kvm/set_memory_region_test.c
> @@ -376,7 +376,7 @@ static void test_add_max_memory_regions(void)
>   	pr_info("Adding slots 0..%i, each memory region with %dK size\n",
>   		(max_mem_slots - 1), MEM_REGION_SIZE >> 10);
> 
> -	mem = mmap(NULL, MEM_REGION_SIZE * max_mem_slots + alignment,
> +	mem = mmap(NULL, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment,
>   		   PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>   	TEST_ASSERT(mem != MAP_FAILED, "Failed to mmap() host");
>   	mem_aligned = (void *)(((size_t) mem + alignment - 1) & ~(alignment - 1));
> @@ -401,7 +401,7 @@ static void test_add_max_memory_regions(void)
>   	TEST_ASSERT(ret == -1 && errno == EINVAL,
>   		    "Adding one more memory slot should fail with EINVAL");
> 
> -	munmap(mem, MEM_REGION_SIZE * max_mem_slots + alignment);
> +	munmap(mem, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment);
>   	munmap(mem_extra, MEM_REGION_SIZE);
>   	kvm_vm_free(vm);
>   }
> 

Re: [PATCH] KVM: selftests: Fix mapping length truncation in m{,un}map()

[Christian Borntraeger]

On 30.06.21 09:37, Christian Borntraeger wrote:
> 
> 
> On 24.06.21 09:09, Zenghui Yu wrote:
>> max_mem_slots is now declared as uint32_t. The result of (0x200000 * 32767)
>> is unexpectedly truncated to be 0xffe00000, whilst we actually need to
>> allocate about, 63GB. Cast max_mem_slots to size_t in both mmap() and
>> munmap() to fix the length truncation.
>>
>> We'll otherwise see the failure on arm64 thanks to the access_ok() checking
>> in __kvm_set_memory_region(), as the unmapped VA happen to go beyond the
>> task's allowed address space.
>>
>>   # ./set_memory_region_test
>> Allowed number of memory slots: 32767
>> Adding slots 0..32766, each memory region with 2048K size
>> ==== Test Assertion Failure ====
>>    set_memory_region_test.c:391: ret == 0
>>    pid=94861 tid=94861 errno=22 - Invalid argument
>>       1    0x00000000004015a7: test_add_max_memory_regions at set_memory_region_test.c:389
>>       2     (inlined by) main at set_memory_region_test.c:426
>>       3    0x0000ffffb8e67bdf: ?? ??:0
>>       4    0x00000000004016db: _start at :?
>>    KVM_SET_USER_MEMORY_REGION IOCTL failed,
>>    rc: -1 errno: 22 slot: 2615
>>
>> Fixes: 3bf0fcd75434 ("KVM: selftests: Speed up set_memory_region_test")
>> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
> 
> While likely correct, this now breaks on many test systems in our CI that have less memory than 64GB.
> (We do get ENOMEM). I have not seen the ENOMEM failures in earlier versions. Strange

As we do not need the memory, the following seems to do the trick (MAP_NORESERVE)


diff --git a/tools/testing/selftests/kvm/set_memory_region_test.c b/tools/testing/selftests/kvm/set_memory_region_test.c
index d8812f27648c..0fc68371fb1b 100644
--- a/tools/testing/selftests/kvm/set_memory_region_test.c
+++ b/tools/testing/selftests/kvm/set_memory_region_test.c
@@ -377,7 +377,7 @@ static void test_add_max_memory_regions(void)
                 (max_mem_slots - 1), MEM_REGION_SIZE >> 10);
  
         mem = mmap(NULL, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment,
-                  PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+                  PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
         TEST_ASSERT(mem != MAP_FAILED, "Failed to mmap() host");
         mem_aligned = (void *)(((size_t) mem + alignment - 1) & ~(alignment - 1));