Re: [PATCH v4 2/2] riscv: selftests: Add a ptrace test to verify syscall parameter modification

[Celeste Liu <uwu@coelacanthus.name>]

On 2024-12-26 21:35, Dmitry V. Levin wrote:
> On Thu, Dec 26, 2024 at 06:52:52PM +0800, Celeste Liu wrote:
>> This test checks that orig_a0 allows a syscall argument to be modified,
>> and that changing a0 does not change the syscall argument.
>>
>> Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
>> Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
>> Co-developed-by: Charlie Jenkins <charlie@rivosinc.com>
>> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
>> Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
>> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
> [...]
>> diff --git a/tools/testing/selftests/riscv/abi/ptrace.c b/tools/testing/selftests/riscv/abi/ptrace.c
>> new file mode 100644
>> index 0000000000000000000000000000000000000000..023695352215bb5de3f91c1a6f5ea3b4f9373ff9
>> --- /dev/null
>> +++ b/tools/testing/selftests/riscv/abi/ptrace.c
> [...]
>> +	if (ptrace(PTRACE_GET_SYSCALL_INFO, pid, PTRACE_SYSCALL_INFO_ENTRY, &syscall_info_entry))
>> +		perr_and_exit("failed to get syscall info of entry\n");
>> +	result->orig_a0 = syscall_info_entry->entry.args[0];
>> +	if (ptrace(PTRACE_GET_SYSCALL_INFO, pid, PTRACE_SYSCALL_INFO_EXIT, &syscall_info_exit))
>> +		perr_and_exit("failed to get syscall info of exit\n");
>> +	result->a0 = syscall_info_exit->exit.rval;
> 
> I'm sorry but this is not how PTRACE_GET_SYSCALL_INFO should be used.
> 
> PTRACE_GET_SYSCALL_INFO operation takes a pointer and a size,
> and in this example instead of size you pass constants 1 and 2, which
> essentially means that both syscall_info_entry->entry.args[0] and
> syscall_info_exit->exit.rval are not going to be assigned
> and would just contain some garbage from the stack.
> 
> Also, PTRACE_GET_SYSCALL_INFO operation returns the number of bytes
> available to be written by the kernel, which is always nonzero on any
> PTRACE_GET_SYSCALL_INFO-capable kernel.  In other words, this example
> will always end up with perr_and_exit() call.
> 
> I wonder how this test was tested before the submission.

Oops... It seems I forget sync the code to test board so it runs with the old code...
The code is completely not tested...
I'm so sorry for my mistake.

I will correct it and test it carefully later...

> 
>