Commit 3390107c authored by Dianzhang Chen's avatar Dianzhang Chen Committed by Kleber Sacilotto de Souza

x86/ptrace: Fix possible spectre-v1 in ptrace_get_debugreg()

BugLink: https://bugs.launchpad.net/bugs/1838467

commit 31a2fbb3 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: default avatarDianzhang Chen <dianzhangchen0@gmail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1561476617-3759-1-git-send-email-dianzhangchen0@gmail.comSigned-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarConnor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: default avatarKhalid Elmously <khalid.elmously@canonical.com>
parent 1f969a41
...@@ -23,6 +23,7 @@ ...@@ -23,6 +23,7 @@
#include <linux/rcupdate.h> #include <linux/rcupdate.h>
#include <linux/export.h> #include <linux/export.h>
#include <linux/context_tracking.h> #include <linux/context_tracking.h>
#include <linux/nospec.h>
#include <asm/uaccess.h> #include <asm/uaccess.h>
#include <asm/pgtable.h> #include <asm/pgtable.h>
...@@ -697,9 +698,11 @@ static unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n) ...@@ -697,9 +698,11 @@ static unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n)
{ {
struct thread_struct *thread = &tsk->thread; struct thread_struct *thread = &tsk->thread;
unsigned long val = 0; unsigned long val = 0;
int index = n;
if (n < HBP_NUM) { 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) if (bp)
val = bp->hw.info.address; val = bp->hw.info.address;
......
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