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rseq: Allow registering RSEQ with slice extension

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Since glibc cares about the number of syscalls required to initialize a new
thread, allow initializing rseq with slice extension on. This avoids having to
do another prctl().

Requested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260121143207.814193010@infradead.org
This commit is contained in:
Peter Zijlstra 2026-01-19 11:23:57 +01:00
parent 830969e782
commit d6200245c7
2 changed files with 12 additions and 3 deletions
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3
include/uapi/linux/rseq.h
View File

@ -19,7 +19,8 @@ enum rseq_cpu_id_state {
};
enum rseq_flags {
RSEQ_FLAG_UNREGISTER = (1 << 0),
RSEQ_FLAG_UNREGISTER = (1 << 0),
RSEQ_FLAG_SLICE_EXT_DEFAULT_ON = (1 << 1),
};
enum rseq_cs_flags_bit {

12
kernel/rseq.c
View File

@ -424,7 +424,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32
return 0;
}
if (unlikely(flags))
if (unlikely(flags & ~(RSEQ_FLAG_SLICE_EXT_DEFAULT_ON)))
return -EINVAL;
if (current->rseq.usrptr) {
@ -459,8 +459,12 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32
if (!access_ok(rseq, rseq_len))
return -EFAULT;
if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION))
if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION)) {
rseqfl |= RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE;
if (rseq_slice_extension_enabled() &&
(flags & RSEQ_FLAG_SLICE_EXT_DEFAULT_ON))
rseqfl |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED;
}
scoped_user_write_access(rseq, efault) {
/*
@ -488,6 +492,10 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32
current->rseq.len = rseq_len;
current->rseq.sig = sig;
#ifdef CONFIG_RSEQ_SLICE_EXTENSION
current->rseq.slice.state.enabled = !!(rseqfl & RSEQ_CS_FLAG_SLICE_EXT_ENABLED);
#endif
/*
* If rseq was previously inactive, and has just been
* registered, ensure the cpu_id_start and cpu_id fields