Commit 3ac6d8c7 authored by Dan Williams's avatar Dan Williams Committed by Ingo Molnar

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

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: default avatarDan 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: default avatarIngo Molnar <mingo@kernel.org>
parent 8e1eb3fa
......@@ -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
......
......@@ -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
/*
......
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