Commit-ID: 3ac6d8c787b835b997eb23e43e09aa0895ef7d58 Gitweb: https://git.kernel.org/tip/3ac6d8c787b835b997eb23e43e09aa0895ef7d58 Author: Dan Williams <dan.j.willi...@intel.com> AuthorDate: Mon, 5 Feb 2018 17:18:11 -0800 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Tue, 6 Feb 2018 11:47:44 +0100
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 <a...@linux.intel.com> Signed-off-by: Dan Williams <dan.j.willi...@intel.com> Cc: <sta...@vger.kernel.org> Cc: Andy Lutomirski <l...@kernel.org> Cc: Borislav Petkov <b...@alien8.de> Cc: Brian Gerst <brge...@gmail.com> Cc: Denys Vlasenko <dvlas...@redhat.com> Cc: H. Peter Anvin <h...@zytor.com> Cc: Josh Poimboeuf <jpoim...@redhat.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/151787989146.7847.15749181712358213254.st...@dwillia2-desk3.amr.corp.intel.com [ Made small improvements to the changelog and the code comments. ] Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/entry/calling.h | 19 +++++++++++++++++++ arch/x86/entry/entry_64.S | 6 +++++- 2 files changed, 24 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h index 3f48f69..f4b129d 100644 --- 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 --- 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 /*
