Commit 2fbd7af5 authored Jan 29, 2018 by Dan Williams Committed by Thomas Gleixner Jan 30, 2018

x86/syscall: Sanitize syscall table de-references under speculation



The syscall table base is a user controlled function pointer in kernel
space. Use array_index_nospec() to prevent any out of bounds speculation.

While retpoline prevents speculating into a userspace directed target it
does not stop the pointer de-reference, the concern is leaking memory
relative to the syscall table base, by observing instruction cache
behavior.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: kernel-hardening@lists.openwall.com
Cc: gregkh@linuxfoundation.org
Cc: Andy Lutomirski <luto@kernel.org>
Cc: alan@linux.intel.com
Link: https://lkml.kernel.org/r/151727417984.33451.1216731042505722161.stgit@dwillia2-desk3.amr.corp.intel.com

parent c7f631cb

arch/x86/entry/common.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -21,6 +21,7 @@
		#include <linux/export.h>
		#include <linux/context_tracking.h>
		#include <linux/user-return-notifier.h>
		#include <linux/nospec.h>
		#include <linux/uprobes.h>
		#include <linux/livepatch.h>
		#include <linux/syscalls.h>
		@@ -282,7 +283,8 @@ __visible void do_syscall_64(struct pt_regs *regs)
		* regs->orig_ax, which changes the behavior of some syscalls.
		*/
		if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
		regs->ax = sys_call_table[nr & __SYSCALL_MASK](
		nr = array_index_nospec(nr & __SYSCALL_MASK, NR_syscalls);
		regs->ax = sys_call_table[nr](
		regs->di, regs->si, regs->dx,
		regs->r10, regs->r8, regs->r9);
		}
		@@ -318,6 +320,7 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
		}

		if (likely(nr < IA32_NR_syscalls)) {
		nr = array_index_nospec(nr, IA32_NR_syscalls);
		/*
		* It's possible that a 32-bit syscall implementation
		* takes a 64-bit parameter but nonetheless assumes that