On 03/06/2018, 03:21 PM, Jiri Slaby wrote:
On 02/23/2018, 07:26 PM, Greg Kroah-Hartman wrote:
4.4-stable review patch. If anyone has any objections, please let me know.
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]
This is not complete IMO, the syscall is indeed there, only written in assembly in 4.4 yet.
So this patch looks like it is missing these two hunks (from my SLE12-SP2 backport):
--- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -184,6 +184,8 @@ entry_SYSCALL_64_fastpath: cmpl $__NR_syscall_max, %eax #endif ja 1f /* return -ENOSYS (already in pt_regs->ax) */
sbb %rcx, %rcx /* array_index_mask_nospec() */and %rcx, %rax
Which is not completely correct either. The preceding comparison should write: cmpl $NR_syscalls, %eax jae 1f to have sbb correctly working even on the last syscall number.
thanks,