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McKenney" , Boqun Feng , "H. Peter Anvin" , Paul Turner , linux-api , Peter Oskolkov Message-ID: <1021959527.83217.1658862705489.JavaMail.zimbra@efficios.com> In-Reply-To: <20220622194617.1155957-2-mathieu.desnoyers@efficios.com> References: <20220622194617.1155957-1-mathieu.desnoyers@efficios.com> <20220622194617.1155957-2-mathieu.desnoyers@efficios.com> Subject: Re: [PATCH 2/2] rseq: Kill process when unknown flags are encountered in ABI structures MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_4304 (ZimbraWebClient - FF100 (Linux)/8.8.15_GA_4304) Thread-Topic: rseq: Kill process when unknown flags are encountered in ABI structures Thread-Index: XBYLrKi9cAv8nErblMXcBK4sHvOViA== Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org ----- On Jun 22, 2022, at 3:46 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote: > 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. Hi Peter, as for the prior patch, would you consider pulling this through the tip tree ? Thanks, Mathieu > > Signed-off-by: Mathieu Desnoyers > --- > kernel/rseq.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/rseq.c b/kernel/rseq.c > index 81d7dc80787b..bda8175f8f99 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; > > /* > -- > 2.30.2 -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com