Commit 28621ec2 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
Browse files

rseq: Add prctl() to enable time slice extensions 



Implement a prctl() so that tasks can enable the time slice extension
mechanism. This fails, when time slice extensions are disabled at compile
time or on the kernel command line and when no rseq pointer is registered
in the kernel.

That allows to implement a single trivial check in the exit to user mode
hotpath, to decide whether the whole mechanism needs to be invoked.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251215155708.858717691@linutronix.de
parent b5b82824

include/linux/rseq.h

+9 −0
Original line number Diff line number Diff line
@@ -163,4 +163,13 @@ void rseq_syscall(struct pt_regs *regs); 
static inline void rseq_syscall(struct pt_regs *regs) { }

#endif /* !CONFIG_DEBUG_RSEQ */



#ifdef CONFIG_RSEQ_SLICE_EXTENSION

int rseq_slice_extension_prctl(unsigned long arg2, unsigned long arg3);

#else /* CONFIG_RSEQ_SLICE_EXTENSION */

static inline int rseq_slice_extension_prctl(unsigned long arg2, unsigned long arg3)

{

	return -ENOTSUPP;

}

#endif /* !CONFIG_RSEQ_SLICE_EXTENSION */



#endif /* _LINUX_RSEQ_H */

include/uapi/linux/prctl.h

+10 −0
Original line number Diff line number Diff line
@@ -386,4 +386,14 @@ struct prctl_mm_map { 
# define PR_FUTEX_HASH_SET_SLOTS	1

# define PR_FUTEX_HASH_GET_SLOTS	2



/* RSEQ time slice extensions */

#define PR_RSEQ_SLICE_EXTENSION			79

# define PR_RSEQ_SLICE_EXTENSION_GET		1

# define PR_RSEQ_SLICE_EXTENSION_SET		2

/*

 * Bits for RSEQ_SLICE_EXTENSION_GET/SET

 * PR_RSEQ_SLICE_EXT_ENABLE:	Enable

 */

# define PR_RSEQ_SLICE_EXT_ENABLE		0x01



#endif /* _LINUX_PRCTL_H */

kernel/rseq.c

+52 −0
Original line number Diff line number Diff line
@@ -71,6 +71,7 @@ 
#define RSEQ_BUILD_SLOW_PATH



#include <linux/debugfs.h>

#include <linux/prctl.h>

#include <linux/ratelimit.h>

#include <linux/rseq_entry.h>

#include <linux/sched.h>
@@ -501,6 +502,57 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32 
#ifdef CONFIG_RSEQ_SLICE_EXTENSION

DEFINE_STATIC_KEY_TRUE(rseq_slice_extension_key);



int rseq_slice_extension_prctl(unsigned long arg2, unsigned long arg3)

{

	switch (arg2) {

	case PR_RSEQ_SLICE_EXTENSION_GET:

		if (arg3)

			return -EINVAL;

		return current->rseq.slice.state.enabled ? PR_RSEQ_SLICE_EXT_ENABLE : 0;



	case PR_RSEQ_SLICE_EXTENSION_SET: {

		u32 rflags, valid = RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE;

		bool enable = !!(arg3 & PR_RSEQ_SLICE_EXT_ENABLE);



		if (arg3 & ~PR_RSEQ_SLICE_EXT_ENABLE)

			return -EINVAL;

		if (!rseq_slice_extension_enabled())

			return -ENOTSUPP;

		if (!current->rseq.usrptr)

			return -ENXIO;



		/* No change? */

		if (enable == !!current->rseq.slice.state.enabled)

			return 0;



		if (get_user(rflags, &current->rseq.usrptr->flags))

			goto die;



		if (current->rseq.slice.state.enabled)

			valid |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED;



		if ((rflags & valid) != valid)

			goto die;



		rflags &= ~RSEQ_CS_FLAG_SLICE_EXT_ENABLED;

		rflags |= RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE;

		if (enable)

			rflags |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED;



		if (put_user(rflags, &current->rseq.usrptr->flags))

			goto die;



		current->rseq.slice.state.enabled = enable;

		return 0;

	}

	default:

		return -EINVAL;

	}

die:

	force_sig(SIGSEGV);

	return -EFAULT;

}



static int __init rseq_slice_cmdline(char *str)

{

	bool on;

kernel/sys.c

+6 −0
Original line number Diff line number Diff line
@@ -53,6 +53,7 @@ 
#include <linux/time_namespace.h>

#include <linux/binfmts.h>

#include <linux/futex.h>

#include <linux/rseq.h>



#include <linux/sched.h>

#include <linux/sched/autogroup.h>
@@ -2868,6 +2869,11 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, 
	case PR_FUTEX_HASH:

		error = futex_hash_prctl(arg2, arg3, arg4);

		break;

	case PR_RSEQ_SLICE_EXTENSION:

		if (arg4 || arg5)

			return -EINVAL;

		error = rseq_slice_extension_prctl(arg2, arg3);

		break;

	default:

		trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);

		error = -EINVAL;