On Wed, Nov 19, 2014 at 08:46:19AM +0000, AKASHI Takahiro wrote:
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 :)
What does x86 do?
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*.
Ok, but now userspace sees -ENOSYS for a skipped system call in that case, whereas it would usually see whatever the trace put in x0, right?
Will