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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