The n in ptrace_get_debugreg() is indirectly controlled by userspace via syscall: ptrace(defined in kernel/ptrace.c), 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 <[email protected]> --- arch/x86/kernel/ptrace.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 4b8ee05..3f8f158 100644 --- 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> @@ -644,7 +645,8 @@ static unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n) unsigned long val = 0; if (n < HBP_NUM) { - struct perf_event *bp = thread->ptrace_bps[n]; + struct perf_event *bp = + thread->ptrace_bps[array_index_nospec(n, HBP_NUM)]; if (bp) val = bp->hw.info.address; -- 2.7.4
