linux-kernel - [tip:x86/urgent] x86/cpu: Fix bootup crashes by sanitizing the argument of the 'clearcpuid=' command-line option

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Date:   Thu, 5 Jan 2017 07:04:49 -0800
From:   tip-bot for Lukasz Odzioba <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, bp@...e.de, tglx@...utronix.de,
        hpa@...or.com, torvalds@...ux-foundation.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org, lukasz.odzioba@...el.com
Subject: [tip:x86/urgent] x86/cpu: Fix bootup crashes by sanitizing the
 argument of the 'clearcpuid=' command-line option

Commit-ID:  dd853fd216d1485ed3045ff772079cc8689a9a4a
Gitweb:     http://git.kernel.org/tip/dd853fd216d1485ed3045ff772079cc8689a9a4a
Author:     Lukasz Odzioba <lukasz.odzioba@...el.com>
AuthorDate: Wed, 28 Dec 2016 14:55:40 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 5 Jan 2017 08:54:34 +0100

x86/cpu: Fix bootup crashes by sanitizing the argument of the 'clearcpuid=' command-line option

A negative number can be specified in the cmdline which will be used as
setup_clear_cpu_cap() argument. With that we can clear/set some bit in
memory predceeding boot_cpu_data/cpu_caps_cleared which may cause kernel
to misbehave. This patch adds lower bound check to setup_disablecpuid().

Boris Petkov reproduced a crash:

  [    1.234575] BUG: unable to handle kernel paging request at ffffffff858bd540
  [    1.236535] IP: memcpy_erms+0x6/0x10

Signed-off-by: Lukasz Odzioba <lukasz.odzioba@...el.com>
Acked-by: Borislav Petkov <bp@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: andi.kleen@...el.com
Cc: bp@...en8.de
Cc: dave.hansen@...ux.intel.com
Cc: luto@...nel.org
Cc: slaoub@...il.com
Fixes: ac72e7888a61 ("x86: add generic clearcpuid=... option")
Link: http://lkml.kernel.org/r/1482933340-11857-1-git-send-email-lukasz.odzioba@intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/cpu/common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index dc1697c..9bab7a8 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1221,7 +1221,7 @@ static __init int setup_disablecpuid(char *arg)
 {
 	int bit;
 
-	if (get_option(&arg, &bit) && bit < NCAPINTS*32)
+	if (get_option(&arg, &bit) && bit >= 0 && bit < NCAPINTS * 32)
 		setup_clear_cpu_cap(bit);
 	else
 		return 0;