linux-kernel - [PATCH 4/5 v2] x86: Allow nesting of the debug stack IDT setting

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20120601150058.256940176@goodmis.org>
Date:	Fri, 01 Jun 2012 10:57:06 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"H. Peter Anvin" <hpa@...or.com>, Dave Jones <davej@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH 4/5 v2] x86: Allow nesting of the debug stack IDT setting

From: Steven Rostedt <srostedt@...hat.com>

When the NMI handler runs, it checks if it preempted a debug handler
and if that handler is using the debug stack. If it is, it changes the
IDT table not to update the stack, otherwise it will reset the debug
stack and corrupt the debug handler it preempted.

Now that ftrace uses breakpoints to change functions from nops to
callers, many more places may hit a breakpoint. Unfortunately this
includes some of the calls that lockdep performs. Which causes issues
with the debug stack. It too needs to change the debug stack before
tracing (if called from the debug handler).

Allow the debug_stack_set_zero() and debug_stack_reset() to be nested
so that the debug handlers can take advantage of them too.

[ Used this_cpu_*() over __get_cpu_var() as suggested by H. Peter Anvin ]

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 arch/x86/kernel/cpu/common.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 82f29e7..6b9333b 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1101,14 +1101,20 @@ int is_debug_stack(unsigned long addr)
 		 addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ));
 }

+static DEFINE_PER_CPU(u32, debug_stack_use_ctr);
+
 void debug_stack_set_zero(void)
 {
+	this_cpu_inc(debug_stack_use_ctr);
 	load_idt((const struct desc_ptr *)&nmi_idt_descr);
 }

 void debug_stack_reset(void)
 {
-	load_idt((const struct desc_ptr *)&idt_descr);
+	if (WARN_ON(!this_cpu_read(debug_stack_use_ctr)))
+		return;
+	if (this_cpu_dec_return(debug_stack_use_ctr) == 0)
+		load_idt((const struct desc_ptr *)&idt_descr);
 }

 #else	/* CONFIG_X86_64 */
-- 
1.7.10

Download attachment "signature.asc" of type "application/pgp-signature" (837 bytes)