Commit ee3e3ac0 authored by Mathieu Desnoyers's avatar Mathieu Desnoyers Committed by Peter Zijlstra
Browse files

rseq: Introduce extensible rseq ABI 



Introduce the extensible rseq ABI, where the feature size supported by
the kernel and the required alignment are communicated to user-space
through ELF auxiliary vectors.

This allows user-space to call rseq registration with a rseq_len of
either 32 bytes for the original struct rseq size (which includes
padding), or larger.

If rseq_len is larger than 32 bytes, then it must be large enough to
contain the feature size communicated to user-space through ELF
auxiliary vectors.

Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221122203932.231377-4-mathieu.desnoyers@efficios.com
parent 317c8194

include/linux/sched.h

+4 −0
Original line number Diff line number Diff line
@@ -1302,6 +1302,7 @@ struct task_struct { 


#ifdef CONFIG_RSEQ

	struct rseq __user *rseq;

	u32 rseq_len;

	u32 rseq_sig;

	/*

	 * RmW on rseq_event_mask must be performed atomically
@@ -2352,10 +2353,12 @@ static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags) 
{

	if (clone_flags & CLONE_VM) {

		t->rseq = NULL;

		t->rseq_len = 0;

		t->rseq_sig = 0;

		t->rseq_event_mask = 0;

	} else {

		t->rseq = current->rseq;

		t->rseq_len = current->rseq_len;

		t->rseq_sig = current->rseq_sig;

		t->rseq_event_mask = current->rseq_event_mask;

	}
@@ -2364,6 +2367,7 @@ static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags) 
static inline void rseq_execve(struct task_struct *t)

{

	t->rseq = NULL;

	t->rseq_len = 0;

	t->rseq_sig = 0;

	t->rseq_event_mask = 0;

}

kernel/ptrace.c

+1 −1
Original line number Diff line number Diff line
@@ -813,7 +813,7 @@ static long ptrace_get_rseq_configuration(struct task_struct *task, 
{

	struct ptrace_rseq_configuration conf = {

		.rseq_abi_pointer = (u64)(uintptr_t)task->rseq,

		.rseq_abi_size = sizeof(*task->rseq),

		.rseq_abi_size = task->rseq_len,

		.signature = task->rseq_sig,

		.flags = 0,

	};

kernel/rseq.c

+30 −7
Original line number Diff line number Diff line
@@ -18,6 +18,9 @@ 
#define CREATE_TRACE_POINTS

#include <trace/events/rseq.h>



/* The original rseq structure size (including padding) is 32 bytes. */

#define ORIG_RSEQ_SIZE		32



#define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT | \

				  RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \

				  RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE)
@@ -87,10 +90,15 @@ static int rseq_update_cpu_id(struct task_struct *t) 
	u32 cpu_id = raw_smp_processor_id();

	struct rseq __user *rseq = t->rseq;



	if (!user_write_access_begin(rseq, sizeof(*rseq)))

	if (!user_write_access_begin(rseq, t->rseq_len))

		goto efault;

	unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end);

	unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end);

	/*

	 * Additional feature fields added after ORIG_RSEQ_SIZE

	 * need to be conditionally updated only if

	 * t->rseq_len != ORIG_RSEQ_SIZE.

	 */

	user_write_access_end();

	trace_rseq_update(t);

	return 0;
@@ -117,6 +125,11 @@ static int rseq_reset_rseq_cpu_id(struct task_struct *t) 
	 */

	if (put_user(cpu_id, &t->rseq->cpu_id))

		return -EFAULT;

	/*

	 * Additional feature fields added after ORIG_RSEQ_SIZE

	 * need to be conditionally reset only if

	 * t->rseq_len != ORIG_RSEQ_SIZE.

	 */

	return 0;

}
@@ -344,7 +357,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, 
		/* Unregister rseq for current thread. */

		if (current->rseq != rseq || !current->rseq)

			return -EINVAL;

		if (rseq_len != sizeof(*rseq))

		if (rseq_len != current->rseq_len)

			return -EINVAL;

		if (current->rseq_sig != sig)

			return -EPERM;
@@ -353,6 +366,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, 
			return ret;

		current->rseq = NULL;

		current->rseq_sig = 0;

		current->rseq_len = 0;

		return 0;

	}
@@ -365,7 +379,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, 
		 * the provided address differs from the prior

		 * one.

		 */

		if (current->rseq != rseq || rseq_len != sizeof(*rseq))

		if (current->rseq != rseq || rseq_len != current->rseq_len)

			return -EINVAL;

		if (current->rseq_sig != sig)

			return -EPERM;
@@ -374,15 +388,24 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, 
	}



	/*

	 * If there was no rseq previously registered,

	 * ensure the provided rseq is properly aligned and valid.

	 * If there was no rseq previously registered, ensure the provided rseq

	 * is properly aligned, as communcated to user-space through the ELF

	 * auxiliary vector AT_RSEQ_ALIGN. If rseq_len is the original rseq

	 * size, the required alignment is the original struct rseq alignment.

	 *

	 * In order to be valid, rseq_len is either the original rseq size, or

	 * large enough to contain all supported fields, as communicated to

	 * user-space through the ELF auxiliary vector AT_RSEQ_FEATURE_SIZE.

	 */

	if (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) ||

	    rseq_len != sizeof(*rseq))

	if (rseq_len < ORIG_RSEQ_SIZE ||

	    (rseq_len == ORIG_RSEQ_SIZE && !IS_ALIGNED((unsigned long)rseq, ORIG_RSEQ_SIZE)) ||

	    (rseq_len != ORIG_RSEQ_SIZE && (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) ||

					    rseq_len < offsetof(struct rseq, end))))

		return -EINVAL;

	if (!access_ok(rseq, rseq_len))

		return -EFAULT;

	current->rseq = rseq;

	current->rseq_len = rseq_len;

	current->rseq_sig = sig;

	/*

	 * If rseq was previously inactive, and has just been