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From: tip-bot for Thomas Gleixner <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: bp@alien8.de, mingo@kernel.org, rjones@redhat.com, hpa@zytor.com,
	tglx@linutronix.de, linux-kernel@vger.kernel.org,
	cebbert.lkml@gmail.com
Subject: [tip:x86/urgent] x86/alternatives: Make optimize_nops() interrupt safe and synced
Date: Thu, 3 Sep 2015 12:30:47 -0700	[thread overview]
Message-ID: <tip-66c117d7fa2ae429911e60d84bf31a90b2b96189@git.kernel.org> (raw)
In-Reply-To: <alpine.DEB.2.11.1509031232340.15006@nanos>

Commit-ID:  66c117d7fa2ae429911e60d84bf31a90b2b96189
Gitweb:     http://git.kernel.org/tip/66c117d7fa2ae429911e60d84bf31a90b2b96189
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Thu, 3 Sep 2015 12:34:55 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 3 Sep 2015 21:27:47 +0200

x86/alternatives: Make optimize_nops() interrupt safe and synced

Richard reported the following crash:

[    0.036000] BUG: unable to handle kernel paging request at 55501e06
[    0.036000] IP: [<c0aae48b>] common_interrupt+0xb/0x38
[    0.036000] Call Trace:
[    0.036000]  [<c0409c80>] ? add_nops+0x90/0xa0
[    0.036000]  [<c040a054>] apply_alternatives+0x274/0x630

Chuck decoded:

 "  0:   8d 90 90 83 04 24       lea    0x24048390(%eax),%edx
    6:   80 fc 0f                cmp    $0xf,%ah
    9:   a8 0f                   test   $0xf,%al
 >> b:   a0 06 1e 50 55          mov    0x55501e06,%al
   10:   57                      push   %edi
   11:   56                      push   %esi

 Interrupt 0x30 occurred while the alternatives code was replacing the
 initial 0x90,0x90,0x90 NOPs (from the ASM_CLAC macro) with the
 optimized version, 0x8d,0x76,0x00. Only the first byte has been
 replaced so far, and it makes a mess out of the insn decoding."

optimize_nops() is buggy in two aspects:

- It's not disabling interrupts across the modification
- It's lacking a sync_core() call

Add both.

Fixes: 4fd4b6e5537c 'x86/alternatives: Use optimized NOPs for padding'
Reported-and-tested-by: "Richard W.M. Jones" <rjones@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Richard W.M. Jones <rjones@redhat.com>
Cc: Chuck Ebbert <cebbert.lkml@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1509031232340.15006@nanos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/alternative.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index c42827e..25f9093 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -338,10 +338,15 @@ done:
 
 static void __init_or_module optimize_nops(struct alt_instr *a, u8 *instr)
 {
+	unsigned long flags;
+
 	if (instr[0] != 0x90)
 		return;
 
+	local_irq_save(flags);
 	add_nops(instr + (a->instrlen - a->padlen), a->padlen);
+	sync_core();
+	local_irq_restore(flags);
 
 	DUMP_BYTES(instr, a->instrlen, "%p: [%d:%d) optimized NOPs: ",
 		   instr, a->instrlen - a->padlen, a->padlen);

  parent reply	other threads:[~2015-09-03 19:31 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-08-31  2:37 [BUG 4.2-rc8] Interrupt occurs while apply_alternatives() is patching the handler Chuck Ebbert
2015-09-01  6:20 ` Richard W.M. Jones
2015-09-02  9:11   ` Thomas Gleixner
2015-09-02 19:05     ` Richard W.M. Jones
2015-09-03  7:53       ` Richard W.M. Jones
2015-09-03  8:50     ` Borislav Petkov
2015-09-03 10:41       ` Thomas Gleixner
2015-09-03 12:43         ` Josh Boyer
2015-09-03 13:01           ` Thomas Gleixner
2015-09-03 15:48         ` Richard W.M. Jones
2015-09-03 19:30         ` tip-bot for Thomas Gleixner [this message]
2015-09-04  7:40         ` Richard W.M. Jones
2015-09-04 12:02         ` Borislav Petkov
2015-09-04 13:37           ` Thomas Gleixner
2015-09-05 15:25             ` Borislav Petkov

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