From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:32918 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751869AbdK0MlY (ORCPT ); Mon, 27 Nov 2017 07:41:24 -0500 Subject: Patch "x86/entry/64: Add missing irqflags tracing to native_load_gs_index()" has been added to the 4.9-stable tree To: luto@kernel.org, bpetkov@suse.de, brgerst@gmail.com, dave.hansen@intel.com, gregkh@linuxfoundation.org, jpoimboe@redhat.com, mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de, torvalds@linux-foundation.org Cc: , From: Date: Mon, 27 Nov 2017 13:41:01 +0100 Message-ID: <1511786461176251@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled x86/entry/64: Add missing irqflags tracing to native_load_gs_index() to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-entry-64-add-missing-irqflags-tracing-to-native_load_gs_index.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From ca37e57bbe0cf1455ea3e84eb89ed04a132d59e1 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 22 Nov 2017 20:39:16 -0800 Subject: x86/entry/64: Add missing irqflags tracing to native_load_gs_index() From: Andy Lutomirski commit ca37e57bbe0cf1455ea3e84eb89ed04a132d59e1 upstream. Running this code with IRQs enabled (where dummy_lock is a spinlock): static void check_load_gs_index(void) { /* This will fail. */ load_gs_index(0xffff); spin_lock(&dummy_lock); spin_unlock(&dummy_lock); } Will generate a lockdep warning. The issue is that the actual write to %gs would cause an exception with IRQs disabled, and the exception handler would, as an inadvertent side effect, update irqflag tracing to reflect the IRQs-off status. native_load_gs_index() would then turn IRQs back on and return with irqflag tracing still thinking that IRQs were off. The dummy lock-and-unlock causes lockdep to notice the error and warn. Fix it by adding the missing tracing. Apparently nothing did this in a context where it mattered. I haven't tried to find a code path that would actually exhibit the warning if appropriately nasty user code were running. I suspect that the security impact of this bug is very, very low -- production systems don't run with lockdep enabled, and the warning is mostly harmless anyway. Found during a quick audit of the entry code to try to track down an unrelated bug that Ingo found in some still-in-development code. Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/e1aeb0e6ba8dd430ec36c8a35e63b429698b4132.1511411918.git.luto@kernel.org Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- arch/x86/entry/entry_64.S | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -54,15 +54,19 @@ ENTRY(native_usergs_sysret64) ENDPROC(native_usergs_sysret64) #endif /* CONFIG_PARAVIRT */ -.macro TRACE_IRQS_IRETQ +.macro TRACE_IRQS_FLAGS flags:req #ifdef CONFIG_TRACE_IRQFLAGS - bt $9, EFLAGS(%rsp) /* interrupts off? */ + bt $9, \flags /* interrupts off? */ jnc 1f TRACE_IRQS_ON 1: #endif .endm +.macro TRACE_IRQS_IRETQ + TRACE_IRQS_FLAGS EFLAGS(%rsp) +.endm + /* * When dynamic function tracer is enabled it will add a breakpoint * to all locations that it is about to modify, sync CPUs, update @@ -868,11 +872,13 @@ idtentry simd_coprocessor_error do_simd ENTRY(native_load_gs_index) pushfq DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI) + TRACE_IRQS_OFF SWAPGS .Lgs_change: movl %edi, %gs 2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE SWAPGS + TRACE_IRQS_FLAGS (%rsp) popfq ret END(native_load_gs_index) Patches currently in stable-queue which might be from luto@kernel.org are queue-4.9/x86-entry-64-add-missing-irqflags-tracing-to-native_load_gs_index.patch