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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Thomas Gleixner" <tglx@linutronix.de>,
        "David Woodhouse" <dwmw@amazon.co.uk>,
        "Borislav Petkov" <bp@alien8.de>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
Message-ID: <lsq.1519831218.291303251@decadent.org.uk>
Subject: [PATCH 3.16 222/254] x86/mce: Make machine check speculation
 protected
In-Reply-To: <lsq.1519831217.271785318@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
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3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Thomas Gleixner <tglx@linutronix.de>

commit 6f41c34d69eb005e7848716bbcafc979b35037d5 upstream.

The machine check idtentry uses an indirect branch directly from the low
level code. This evades the speculation protection.

Replace it by a direct call into C code and issue the indirect call there
so the compiler can apply the proper speculation protection.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by:Borislav Petkov <bp@alien8.de>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Niced-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801181626290.1847@nanos
[bwh: Backported to 3.16
 - #include <asm/traps.h> in mce.c
 - Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -91,6 +91,7 @@ dotraplinkage void do_simd_coprocessor_e
 #ifdef CONFIG_X86_32
 dotraplinkage void do_iret_error(struct pt_regs *, long);
 #endif
+dotraplinkage void do_mce(struct pt_regs *, long);
 
 static inline int get_si_code(unsigned long condition)
 {
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -46,6 +46,7 @@
 #include <asm/tlbflush.h>
 #include <asm/mce.h>
 #include <asm/msr.h>
+#include <asm/traps.h>
 
 #include "mce-internal.h"
 
@@ -1693,6 +1694,11 @@ static void unexpected_machine_check(str
 void (*machine_check_vector)(struct pt_regs *, long error_code) =
 						unexpected_machine_check;
 
+dotraplinkage void do_mce(struct pt_regs *regs, long error_code)
+{
+	machine_check_vector(regs, error_code);
+}
+
 /*
  * Called for each booted CPU to set up machine checks.
  * Must be called with preempt off:
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1320,7 +1320,7 @@ trace_idtentry page_fault do_page_fault
 idtentry async_page_fault do_async_page_fault has_error_code=1
 #endif
 #ifdef CONFIG_X86_MCE
-idtentry machine_check has_error_code=0 paranoid=1 do_sym=*machine_check_vector(%rip)
+idtentry machine_check		do_mce			has_error_code=0	paranoid=1
 #endif
 
 	/*