Commit 8cb3ed13 authored Sep 22, 2009 by Roland McGrath

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>

parent 08ff18e2

arch/x86/kernel/ptrace.c

+13 −1

Original line number	Diff line number	Diff line
		@@ -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);

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