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@xxxxxxxxx> >> >> (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@xxxxxxxxxxxxxxxxxxxx> >> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> >> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> >> Cc: linux-arch@xxxxxxxxxxxxxxx >> Cc: kernel-hardening@xxxxxxxxxxxxxxxxxx >> Cc: gregkh@xxxxxxxxxxxxxxxxxxx >> Cc: Andy Lutomirski <luto@xxxxxxxxxx> >> Cc: alan@xxxxxxxxxxxxxxx >> Link: https://lkml.kernel.org/r/151727417984.33451.1216731042505722161.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx >> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> >> [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, -- js suse labs
