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rseq: Kill process when unknown flags are encountered in ABI structures

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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 <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20220622194617.1155957-2-mathieu.desnoyers@efficios.com
This commit is contained in:
Mathieu Desnoyers 2022-06-22 15:46:17 -04:00 committed by Ingo Molnar
parent 0190e4198e
commit c17a6ff932
1 changed files with 2 additions and 2 deletions
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4
kernel/rseq.c
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@ -176,7 +176,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
u32 flags, event_mask; u32 flags, event_mask;
int ret; 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; return -EINVAL;
/* Get thread flags. */ /* Get thread flags. */
@ -184,7 +184,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
if (ret) if (ret)
return 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; return -EINVAL;
/* /*