linux-kernel - [PATCH 3.16 181/370] x86/cpu: Fix bootup crashes by sanitizing the argument of the 'clearcpuid=' command-line option

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Message-ID: <lsq.1489146382.835762965@decadent.org.uk>
Date:   Fri, 10 Mar 2017 11:46:22 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, andi.kleen@...el.com, luto@...nel.org,
        "Borislav Petkov" <bp@...e.de>,
        "Lukasz Odzioba" <lukasz.odzioba@...el.com>,
        "Ingo Molnar" <mingo@...nel.org>, slaoub@...il.com, bp@...en8.de,
        "Peter Zijlstra" <peterz@...radead.org>,
        dave.hansen@...ux.intel.com,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Thomas Gleixner" <tglx@...utronix.de>
Subject: [PATCH 3.16 181/370] x86/cpu: Fix bootup crashes by sanitizing
 the argument of the 'clearcpuid=' command-line option

3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Lukasz Odzioba <lukasz.odzioba@...el.com>

commit dd853fd216d1485ed3045ff772079cc8689a9a4a upstream.

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>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kernel/cpu/common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1105,7 +1105,7 @@ static __init int setup_disablecpuid(cha
 {
 	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;