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Commit 68ff2829 authored by Dianzhang Chen's avatar Dianzhang Chen Committed by Greg Kroah-Hartman
Browse files

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



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: 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.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d8e26651

arch/x86/kernel/ptrace.c

+4 −1
Original line number Diff line number Diff line
@@ -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 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];

		struct perf_event *bp = thread->ptrace_bps[index];

		index = array_index_nospec(index, HBP_NUM);



		if (bp)

			val = bp->hw.info.address;