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x86: ptrace: set TS_COMPAT when 32-bit ptrace sets orig_eax>=0 

The 32-bit ptrace syscall on a 64-bit kernel (32-bit debugger on
32-bit task) behaves differently than a native 32-bit kernel.  When
setting a register state of orig_eax>=0 and eax=-ERESTART* when the
debugged task is NOT on its way out of a 32-bit syscall, the task will
fail to do the syscall restart logic that it should do.

Test case available at http://sources.redhat.com/cgi-bin/cvsweb.cgi/~checkout~/tests/ptrace-tests/tests/erestartsys-trap.c?cvsroot=systemtap

This happens because the 32-bit ptrace syscall sets eax=0xffffffff
when it sets orig_eax>=0.  The resuming task will not sign-extend this
for the -ERESTART* check because TS_COMPAT is not set.  (So the task
thinks it is restarting after a 64-bit syscall, not a 32-bit one.)

The fix is to have 32-bit ptrace calls set TS_COMPAT when setting
orig_eax>=0.  This ensures that the 32-bit syscall restart logic
will apply when the child resumes.

Signed-off-by: Roland McGrath <roland@redhat.com>
This commit is contained in:
Roland McGrath 2009-09-22 20:12:07 -07:00
parent 08ff18e299
commit 8cb3ed1393
1 changed files with 13 additions and 1 deletions
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14
arch/x86/kernel/ptrace.c
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@ -1111,10 +1111,22 @@ static int putreg32(struct task_struct *child, unsigned regno, u32 value)
R32(esi, si);
R32(ebp, bp);
R32(eax, ax);
R32(orig_eax, orig_ax);
R32(eip, ip);
R32(esp, sp);
case offsetof(struct user32, regs.orig_eax):
/*
* A 32-bit debugger setting orig_eax means to restore
* the state of the task restarting a 32-bit syscall.
* Make sure we interpret the -ERESTART* codes correctly
* in case the task is not actually still sitting at the
* exit from a 32-bit syscall with TS_COMPAT still set.
*/
regs->orig_ax = value;
if (syscall_get_nr(child, regs) >= 0)
task_thread_info(child)->status |= TS_COMPAT;
break;
case offsetof(struct user32, regs.eflags):
return set_flags(child, value);