x86/entry/64: Clear registers for exceptions/interrupts, to reduce speculation attack...

Clear the 'extra' registers on entering the 64-bit kernel for exceptions
and interrupts. The common registers are not cleared since they are
likely clobbered well before they can be exploited in a speculative
execution attack.

Originally-From: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: <stable@vger.kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/151787989146.7847.15749181712358213254.stgit@dwillia2-desk3.amr.corp.intel.com
[ Made small improvements to the changelog and the code comments. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 3f48f69..f4b129d 100644 (file)
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -147,6 +147,25 @@ For 32-bit we have the following conventions - kernel is built with
        UNWIND_HINT_REGS offset=\offset
        .endm
 
+       /*
+        * Sanitize registers of values that a speculation attack
+        * might otherwise want to exploit. The lower registers are
+        * likely clobbered well before they could be put to use in
+        * a speculative execution gadget:
+        */
+       .macro CLEAR_REGS_NOSPEC
+       xorl %ebp, %ebp
+       xorl %ebx, %ebx
+       xorq %r8, %r8
+       xorq %r9, %r9
+       xorq %r10, %r10
+       xorq %r11, %r11
+       xorq %r12, %r12
+       xorq %r13, %r13
+       xorq %r14, %r14
+       xorq %r15, %r15
+       .endm
+
        .macro POP_EXTRA_REGS
        popq %r15
        popq %r14

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 065a71b..9e48002 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -575,6 +575,7 @@ END(irq_entries_start)
        ALLOC_PT_GPREGS_ON_STACK
        SAVE_C_REGS
        SAVE_EXTRA_REGS
+       CLEAR_REGS_NOSPEC
        ENCODE_FRAME_POINTER
 
        testb   $3, CS(%rsp)
@@ -1133,6 +1134,7 @@ ENTRY(xen_failsafe_callback)
        ALLOC_PT_GPREGS_ON_STACK
        SAVE_C_REGS
        SAVE_EXTRA_REGS
+       CLEAR_REGS_NOSPEC
        ENCODE_FRAME_POINTER
        jmp     error_exit
 END(xen_failsafe_callback)
@@ -1178,6 +1180,7 @@ ENTRY(paranoid_entry)
        cld
        SAVE_C_REGS 8
        SAVE_EXTRA_REGS 8
+       CLEAR_REGS_NOSPEC
        ENCODE_FRAME_POINTER 8
        movl    $1, %ebx
        movl    $MSR_GS_BASE, %ecx
@@ -1230,8 +1233,8 @@ ENTRY(error_entry)
        cld
        SAVE_C_REGS 8
        SAVE_EXTRA_REGS 8
+       CLEAR_REGS_NOSPEC
        ENCODE_FRAME_POINTER 8
-       xorl    %ebx, %ebx
        testb   $3, CS+8(%rsp)
        jz      .Lerror_kernelspace
 
@@ -1428,6 +1431,7 @@ ENTRY(nmi)
        pushq   %r14            /* pt_regs->r14 */
        pushq   %r15            /* pt_regs->r15 */
        UNWIND_HINT_REGS
+       CLEAR_REGS_NOSPEC
        ENCODE_FRAME_POINTER
 
        /*