From: Oleg Nesterov <oleg@redhat.com>
Date: Thu, 27 Jun 2013 23:53:48 +0000 (+1000)
Subject: ptrace/x86: ptrace_write_dr7() should create bp if !disabled
X-Git-Tag: next-20130628~3^2~121
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=cd217e369476f1576e8eef8e7db65e0dd53f16a0;p=karo-tx-linux.git

ptrace/x86: ptrace_write_dr7() should create bp if !disabled

24f1e32c ("hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf
events") introduced the minor regression.  Before this commit

	PTRACE_POKEUSER DR7, enableDR0
	PTRACE_POKEUSER DR0, address

was perfectly valid, now PTRACE_POKEUSER(DR7) fails if DR0 was not
previously initialized by PTRACE_POKEUSER(DR0).

Change ptrace_write_dr7() to do ptrace_register_breakpoint(addr => 0) if
!bp && !disabled.  This fixes watchpoint-zeroaddr from ptrace-tests, see
https://bugzilla.redhat.com/show_bug.cgi?id=660204.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Jan Kratochvil <jan.kratochvil@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 052636801b41..5c387b3dce3f 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -670,13 +670,16 @@ restore:
 		if (!bp) {
 			if (disabled)
 				continue;
-			/*
-			 * We should have at least an inactive breakpoint at
-			 * this slot. It means the user is writing dr7 without
-			 * having written the address register first.
-			 */
-			rc = -EINVAL;
-			break;
+
+			bp = ptrace_register_breakpoint(tsk,
+					len, type, 0, disabled);
+			if (IS_ERR(bp)) {
+				rc = PTR_ERR(bp);
+				break;
+			}
+
+			thread->ptrace_bps[i] = bp;
+			continue;
 		}
 
 		rc = ptrace_modify_breakpoint(bp, len, type, disabled);