From 8cb3ed13935b9b523c2de7afc8f68473fe1d4531 Mon Sep 17 00:00:00 2001 From: Roland McGrath Date: Tue, 22 Sep 2009 20:12:07 -0700 Subject: [PATCH] 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 --- arch/x86/kernel/ptrace.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 52222fab99f4..7b058a2dc66a 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -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); -- 2.20.1