4.4-stable review patch. If anyone has any objections, please let me know.
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From: Dan Williams dan.j.williams@intel.com
(cherry picked from commit 2fbd7af5af8665d18bcefae3e9700be07e22b681)
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@dwill... Signed-off-by: David Woodhouse dwmw@amazon.co.uk [jwang: port to 4.4, no syscall_64] Signed-off-by: Jack Wang jinpu.wang@profitbricks.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/entry/common.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -20,6 +20,7 @@ #include <linux/export.h> #include <linux/context_tracking.h> #include <linux/user-return-notifier.h> +#include <linux/nospec.h> #include <linux/uprobes.h>
#include <asm/desc.h> @@ -381,6 +382,7 @@ __always_inline void do_syscall_32_irqs_ }
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