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Subject[PATCH v2] x86/ptrace: Fix possible spectre-v1 in ptrace_get_debugreg()
Date
The index to access the threads ptrace_bps is controlled by userspace
via syscall: sys_ptrace(), hence, hence leading to a potential
exploitation of the Spectre variant 1 vulnerability.
The n can be controlled from:
ptrace -> arch_ptrace -> ptrace_get_debugreg.

Fix this by sanitizing n before using it to index thread->ptrace_bps.

Signed-off-by: Dianzhang Chen <dianzhangchen0@gmail.com>
---
arch/x86/kernel/ptrace.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index a166c96..cbac646 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -25,6 +25,7 @@
#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>
@@ -643,9 +644,11 @@ static unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n)
{
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];
+ index = array_index_nospec(index, HBP_NUM);
+ struct perf_event *bp = thread->ptrace_bps[index];

if (bp)
val = bp->hw.info.address;
--
2.7.4
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