From: Dianzhang Chen <dianzhangchen0@xxxxxxxxx>
commit 31a2fbb390fee4231281b939e1979e810f945415 upstream.
The index to access the threads ptrace_bps is controlled by userspace via
syscall: sys_ptrace(), hence leading to a potential exploitation of the
Spectre variant 1 vulnerability.
The index can be controlled from:
ptrace -> arch_ptrace -> ptrace_get_debugreg.
Fix this by sanitizing the user supplied index before using it access
thread->ptrace_bps.
Signed-off-by: Dianzhang Chen <dianzhangchen0@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: bp@xxxxxxxxx
Cc: hpa@xxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/1561476617-3759-1-git-send-email-dianzhangchen0@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/ptrace.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -24,6 +24,7 @@
#include <linux/rcupdate.h>
#include <linux/export.h>
#include <linux/context_tracking.h>
+#include <linux/nospec.h>
#include <linux/uaccess.h>
#include <asm/pgtable.h>
@@ -651,9 +652,11 @@ static unsigned long ptrace_get_debugreg
{
struct thread_struct *thread = &tsk->thread;
unsigned long val = 0;
+ int index = n;
if (n < HBP_NUM) {
- struct perf_event *bp = thread->ptrace_bps[n];
+ struct perf_event *bp = thread->ptrace_bps[index];
+ index = array_index_nospec(index, HBP_NUM);
if (bp)
val = bp->hw.info.address;
