The syscall table base is a user controlled function pointer in kernel
space. Use 'array_idx' 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>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
arch/x86/entry/common.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 03505ffbe1b6..f78bf8bfdfae 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -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>
@@ -284,6 +285,7 @@ __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)) {
+ nr = array_idx(nr & __SYSCALL_MASK, NR_syscalls);
regs->ax = sys_call_table[nr & __SYSCALL_MASK](
regs->di, regs->si, regs->dx,
regs->r10, regs->r8, regs->r9);
@@ -320,6 +322,7 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
}
if (likely(nr < IA32_NR_syscalls)) {
+ nr = array_idx(nr, IA32_NR_syscalls);
/*
* It's possible that a 32-bit syscall implementation
* takes a 64-bit parameter but nonetheless assumes that
