From c17a6ff9321355487d7d5ccaa7d406a0ea06b6c4 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Wed, 22 Jun 2022 15:46:17 -0400 Subject: [PATCH] rseq: Kill process when unknown flags are encountered in ABI structures rseq_abi()->flags and rseq_abi()->rseq_cs->flags 29 upper bits are currently unused. The current behavior when those bits are set is to ignore them. This is not an ideal behavior, because when future features will start using those flags, if user-space fails to correctly validate that the kernel indeed supports those flags (e.g. with a new sys_rseq flags bit) before using them, it may incorrectly assume that the kernel will handle those flags way when in fact those will be silently ignored on older kernels. Validating that unused flags bits are cleared will allow a smoother transition when those flags will start to be used by allowing applications to fail early, and obviously, when they attempt to use the new flags on an older kernel that does not support them. Signed-off-by: Mathieu Desnoyers Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lkml.kernel.org/r/20220622194617.1155957-2-mathieu.desnoyers@efficios.com --- kernel/rseq.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rseq.c b/kernel/rseq.c index 81d7dc8..bda8175 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -176,7 +176,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags) u32 flags, event_mask; int ret; - if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS)) + if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS) || cs_flags) return -EINVAL; /* Get thread flags. */ @@ -184,7 +184,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags) if (ret) return ret; - if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS)) + if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS) || flags) return -EINVAL; /* -- 2.7.4