4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Jiri Slaby <[email protected]> In 4.4.118, we have commit c8961332d6da (x86/syscall: Sanitize syscall table de-references under speculation), which is a backport of upstream commit 2fbd7af5af86. But it fixed only the C part of the upstream patch -- the IA32 sysentry. So it ommitted completely the assembly part -- the 64bit sysentry. Fix that in this patch by explicit array_index_mask_nospec written in assembly. The same was used in lib/getuser.S. However, to have "sbb" working properly, we have to switch from "cmp" against (NR_syscalls-1) to (NR_syscalls), otherwise the last syscall number would be "and"ed by 0. It is because the original "ja" relies on "CF" or "ZF", but we rely only on "CF" in "sbb". That means: switch to "jae" conditional jump too. Final note: use rcx for mask as this is exactly what is overwritten by the 4th syscall argument (r10) right after. Reported-by: Jan Beulich <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Dan Williams <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: Andy Lutomirski <[email protected]> Cc: [email protected] Cc: Jinpu Wang <[email protected]> Signed-off-by: Jiri Slaby <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- arch/x86/entry/entry_64.S | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -178,12 +178,14 @@ GLOBAL(entry_SYSCALL_64_after_swapgs) jnz tracesys entry_SYSCALL_64_fastpath: #if __SYSCALL_MASK == ~0 - cmpq $__NR_syscall_max, %rax + cmpq $NR_syscalls, %rax #else andl $__SYSCALL_MASK, %eax - cmpl $__NR_syscall_max, %eax + cmpl $NR_syscalls, %eax #endif - ja 1f /* return -ENOSYS (already in pt_regs->ax) */ + jae 1f /* return -ENOSYS (already in pt_regs->ax) */ + sbb %rcx, %rcx /* array_index_mask_nospec() */ + and %rcx, %rax movq %r10, %rcx #ifdef CONFIG_RETPOLINE movq sys_call_table(, %rax, 8), %rax @@ -276,12 +278,14 @@ tracesys_phase2: RESTORE_C_REGS_EXCEPT_RAX RESTORE_EXTRA_REGS #if __SYSCALL_MASK == ~0 - cmpq $__NR_syscall_max, %rax + cmpq $NR_syscalls, %rax #else andl $__SYSCALL_MASK, %eax - cmpl $__NR_syscall_max, %eax + cmpl $NR_syscalls, %eax #endif - ja 1f /* return -ENOSYS (already in pt_regs->ax) */ + jae 1f /* return -ENOSYS (already in pt_regs->ax) */ + sbb %rcx, %rcx /* array_index_mask_nospec() */ + and %rcx, %rax movq %r10, %rcx /* fixup for C */ #ifdef CONFIG_RETPOLINE movq sys_call_table(, %rax, 8), %rax
