linux-kernel - [tip:x86/pti] x86/mce: Make machine check speculation protected

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Date:   Fri, 19 Jan 2018 07:46:55 -0800
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, dwmw@...zon.co.uk, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, peterz@...radead.org, hpa@...or.com
Subject: [tip:x86/pti] x86/mce: Make machine check speculation protected

Commit-ID:  6f41c34d69eb005e7848716bbcafc979b35037d5
Gitweb:     https://git.kernel.org/tip/6f41c34d69eb005e7848716bbcafc979b35037d5
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Thu, 18 Jan 2018 16:28:26 +0100
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 19 Jan 2018 16:31:28 +0100

x86/mce: Make machine check speculation protected

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@...utronix.de>
Reviewed-by:Borislav Petkov <bp@...en8.de>
Reviewed-by: David Woodhouse <dwmw@...zon.co.uk>
Niced-by: Peter Zijlstra <peterz@...radead.org>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801181626290.1847@nanos

---
 arch/x86/entry/entry_64.S        | 2 +-
 arch/x86/include/asm/traps.h     | 1 +
 arch/x86/kernel/cpu/mcheck/mce.c | 5 +++++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index d54a0ed..63f4320 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1258,7 +1258,7 @@ 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
 
 /*
diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 31051f3..3de6933 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -88,6 +88,7 @@ dotraplinkage void do_simd_coprocessor_error(struct pt_regs *, long);
 #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)
 {
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 3b413065..a9e898b 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1788,6 +1788,11 @@ static void unexpected_machine_check(struct pt_regs *regs, long error_code)
 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: