diff mbox series

[bpf-next,3/5] selftests/bpf: don't mask result of bpf_csum_diff() in test_verifier

Message ID 20241021122112.101513-4-puranjay@kernel.org (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series Optimize bpf_csum_diff() and homogenize for all archs | expand

Checks

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bpf/vmtest-bpf-next-PR success PR summary
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 5 this patch: 5
netdev/build_tools success Errors and warnings before: 0 (+1) this patch: 0 (+1)
netdev/cc_maintainers warning 1 maintainers not CCed: linux-kselftest@vger.kernel.org
netdev/build_clang success Errors and warnings before: 5 this patch: 5
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 3 this patch: 3
netdev/checkpatch fail ERROR: spaces required around that '%=' (ctx:VxO) ERROR: spaces required around that ':' (ctx:OxW)
netdev/build_clang_rust success No Rust files in patch. Skipping build
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Commit Message

Puranjay Mohan Oct. 21, 2024, 12:21 p.m. UTC 
The bpf_csum_diff() helper has been fixed to return a 16-bit value for
all archs, so now we don't need to mask the result.

This commit is basically reverting the below:

commit 6185266c5a85 ("selftests/bpf: Mask bpf_csum_diff() return value
to 16 bits in test_verifier")

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
---
 tools/testing/selftests/bpf/progs/verifier_array_access.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Comments

Helge Deller Oct. 21, 2024, 1:01 p.m. UTC | #1 
On 10/21/24 14:21, Puranjay Mohan wrote:
> The bpf_csum_diff() helper has been fixed to return a 16-bit value for
> all archs, so now we don't need to mask the result.
>
> ...
> --- a/tools/testing/selftests/bpf/progs/verifier_array_access.c
> +++ b/tools/testing/selftests/bpf/progs/verifier_array_access.c
> @@ -368,8 +368,7 @@ __naked void a_read_only_array_2_1(void)
>   	r4 = 0;						\
>   	r5 = 0;						\
>   	call %[bpf_csum_diff];				\
> -l0_%=:	r0 &= 0xffff;					\
> -	exit;						\
> +l0_%=:	exit;						\

Instead of dropping the masking, would it make sense to
check here if (r0 >> 16) == 0 ?

Helge
Puranjay Mohan Oct. 21, 2024, 1:14 p.m. UTC | #2 
Helge Deller <deller@gmx.de> writes:

> On 10/21/24 14:21, Puranjay Mohan wrote:
>> The bpf_csum_diff() helper has been fixed to return a 16-bit value for
>> all archs, so now we don't need to mask the result.
>>
>> ...
>> --- a/tools/testing/selftests/bpf/progs/verifier_array_access.c
>> +++ b/tools/testing/selftests/bpf/progs/verifier_array_access.c
>> @@ -368,8 +368,7 @@ __naked void a_read_only_array_2_1(void)
>>   	r4 = 0;						\
>>   	r5 = 0;						\
>>   	call %[bpf_csum_diff];				\
>> -l0_%=:	r0 &= 0xffff;					\
>> -	exit;						\
>> +l0_%=:	exit;						\
>
> Instead of dropping the masking, would it make sense to
> check here if (r0 >> 16) == 0 ?

We define the expected value in R0 to be 65507(0xffe3) in the line at the top:
__success __retval(65507)

So, we should just not do anything to R0 and it should contain this value
after returning from bpf_csum_diff()

This masking hack was added in:

6185266c5a853 ("selftests/bpf: Mask bpf_csum_diff() return value to 16 bits in test_verifier")

because without the fix in patch 2 bpf_csum_diff() would return the
following for this test:

x86                    :    -29 : 0xffffffe3
generic (arm64, riscv) :  65507 : 0x0000ffe3


Thanks,
Puranjay
Daniel Borkmann Oct. 21, 2024, 1:42 p.m. UTC | #3 
On 10/21/24 2:21 PM, Puranjay Mohan wrote:
> The bpf_csum_diff() helper has been fixed to return a 16-bit value for
> all archs, so now we don't need to mask the result.
> 
> This commit is basically reverting the below:
> 
> commit 6185266c5a85 ("selftests/bpf: Mask bpf_csum_diff() return value
> to 16 bits in test_verifier")
> 
> Signed-off-by: Puranjay Mohan <puranjay@kernel.org>

Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Helge Deller Oct. 21, 2024, 2:04 p.m. UTC | #4 
On 10/21/24 15:14, Puranjay Mohan wrote:
> Helge Deller <deller@gmx.de> writes:
>
>> On 10/21/24 14:21, Puranjay Mohan wrote:
>>> The bpf_csum_diff() helper has been fixed to return a 16-bit value for
>>> all archs, so now we don't need to mask the result.
>>>
>>> ...
>>> --- a/tools/testing/selftests/bpf/progs/verifier_array_access.c
>>> +++ b/tools/testing/selftests/bpf/progs/verifier_array_access.c
>>> @@ -368,8 +368,7 @@ __naked void a_read_only_array_2_1(void)
>>>    	r4 = 0;						\
>>>    	r5 = 0;						\
>>>    	call %[bpf_csum_diff];				\
>>> -l0_%=:	r0 &= 0xffff;					\
>>> -	exit;						\
>>> +l0_%=:	exit;						\
>>
>> Instead of dropping the masking, would it make sense to
>> check here if (r0 >> 16) == 0 ?
>
> We define the expected value in R0 to be 65507(0xffe3) in the line at the top:
> __success __retval(65507)
>
> So, we should just not do anything to R0 and it should contain this value
> after returning from bpf_csum_diff()
>
> This masking hack was added in:
>
> 6185266c5a853 ("selftests/bpf: Mask bpf_csum_diff() return value to 16 bits in test_verifier")
>
> because without the fix in patch 2 bpf_csum_diff() would return the
> following for this test:
>
> x86                    :    -29 : 0xffffffe3
> generic (arm64, riscv) :  65507 : 0x0000ffe3

You're right.
Thanks for explaining.

Helge
Toke Høiland-Jørgensen Oct. 22, 2024, 9:55 a.m. UTC | #5 
Puranjay Mohan <puranjay@kernel.org> writes:

> The bpf_csum_diff() helper has been fixed to return a 16-bit value for
> all archs, so now we don't need to mask the result.
>
> This commit is basically reverting the below:
>
> commit 6185266c5a85 ("selftests/bpf: Mask bpf_csum_diff() return value
> to 16 bits in test_verifier")
>
> Signed-off-by: Puranjay Mohan <puranjay@kernel.org>

Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
diff mbox series

Patch

diff --git a/tools/testing/selftests/bpf/progs/verifier_array_access.c b/tools/testing/selftests/bpf/progs/verifier_array_access.c
index 95d7ecc12963b..4195aa824ba55 100644
--- a/tools/testing/selftests/bpf/progs/verifier_array_access.c
+++ b/tools/testing/selftests/bpf/progs/verifier_array_access.c
@@ -368,8 +368,7 @@  __naked void a_read_only_array_2_1(void)
 	r4 = 0;						\
 	r5 = 0;						\
 	call %[bpf_csum_diff];				\
-l0_%=:	r0 &= 0xffff;					\
-	exit;						\
+l0_%=:	exit;						\
 "	:
 	: __imm(bpf_csum_diff),
 	  __imm(bpf_map_lookup_elem),