[PATCH v8 2/6] arm64: ptrace: allow tracer to skip a system call
AKASHI Takahiro
takahiro.akashi at linaro.org
Wed Nov 19 00:46:19 PST 2014
On 11/18/2014 11:04 PM, Will Deacon wrote:
> On Tue, Nov 18, 2014 at 01:10:34AM +0000, AKASHI Takahiro wrote:
>>
>> + if (((int)regs->syscallno == -1) && (orig_syscallno == -1)) {
>> + /*
>> + * user-issued syscall(-1):
>> + * RESTRICTION: We always return ENOSYS whatever value is
>> + * stored in x0 (a return value) at this point.
>> + * Normally, with ptrace off, syscall(-1) returns -ENOSYS.
>> + * With ptrace on, however, if a tracer didn't pay any
>> + * attention to user-issued syscall(-1) and just let it go
>> + * without a hack here, it would return a value in x0 as in
>> + * other system call cases. This means that this system call
>> + * might succeed and see any bogus return value.
>> + * This should be definitely avoided.
>> + */
>> + regs->regs[0] = -ENOSYS;
>> + }
>
> I'm still really uncomfortable with this, and it doesn't seem to match what
> arch/arm/ does either.
Yeah, I know but
as I mentioned before, syscall(-1) will be signaled on arm, and so we don't
have to care about a return value :)
> Doesn't it also prevent a tracer from skipping syscall(-1)?
Syscall(-1) will return -ENOSYS whether or not a syscallno is explicitly replaced with -1
by a tracer, and, in this sense, it is *skipped*.
-Takahiro AKASHI
> Will
>
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