[PATCH 3.2 112/140] x86/mce: Make machine check speculation protected

[Ben Hutchings]

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

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

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
Reviewed-by:Borislav Petkov <bp@xxxxxxxxx>
Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Niced-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801181626290.1847@nanos
[bwh: Backported to 3.2:
 - Don't use dotraplinkage
 - Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/traps.h     | 1 +
 arch/x86/kernel/cpu/mcheck/mce.c | 5 +++++
 arch/x86/kernel/entry_64.S       | 2 +-
 3 files changed, 7 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -69,6 +69,7 @@ dotraplinkage void do_simd_coprocessor_e
 #ifdef CONFIG_X86_32
 dotraplinkage void do_iret_error(struct pt_regs *, long);
 #endif
+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
@@ -1407,6 +1407,11 @@ static void unexpected_machine_check(str
 void (*machine_check_vector)(struct pt_regs *, long error_code) =
 						unexpected_machine_check;
 
+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
@@ -1399,7 +1399,7 @@ errorentry page_fault do_page_fault
 errorentry async_page_fault do_async_page_fault
 #endif
 #ifdef CONFIG_X86_MCE
-paranoidzeroentry machine_check *machine_check_vector(%rip)
+paranoidzeroentry machine_check do_mce
 #endif
 
 	/*