Commit bfdf4e62 authored by Mathieu Desnoyers's avatar Mathieu Desnoyers Committed by Peter Zijlstra
Browse files

rseq: Remove broken uapi field layout on 32-bit little endian 



The rseq rseq_cs.ptr.{ptr32,padding} uapi endianness handling is
entirely wrong on 32-bit little endian: a preprocessor logic mistake
wrongly uses the big endian field layout on 32-bit little endian
architectures.

Fortunately, those ptr32 accessors were never used within the kernel,
and only meant as a convenience for user-space.

Remove those and replace the whole rseq_cs union by a __u64 type, as
this is the only thing really needed to express the ABI. Document how
32-bit architectures are meant to interact with this field.

Fixes: ec9c82e0 ("rseq: uapi: Declare rseq_cs field as union, update includes")
Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220127152720.25898-1-mathieu.desnoyers@efficios.com
parent 5c105d55

include/uapi/linux/rseq.h

+4 −16
Original line number Diff line number Diff line
@@ -105,23 +105,11 @@ struct rseq { 
	 * Read and set by the kernel. Set by user-space with single-copy

	 * atomicity semantics. This field should only be updated by the

	 * thread which registered this data structure. Aligned on 64-bit.

	 *

	 * 32-bit architectures should update the low order bits of the

	 * rseq_cs field, leaving the high order bits initialized to 0.

	 */

	union {

		__u64 ptr64;

#ifdef __LP64__

		__u64 ptr;

#else

		struct {

#if (defined(__BYTE_ORDER) && (__BYTE_ORDER == __BIG_ENDIAN)) || defined(__BIG_ENDIAN)

			__u32 padding;		/* Initialized to zero. */

			__u32 ptr32;

#else /* LITTLE */

			__u32 ptr32;

			__u32 padding;		/* Initialized to zero. */

#endif /* ENDIAN */

		} ptr;

#endif

	} rseq_cs;

	__u64 rseq_cs;



	/*

	 * Restartable sequences flags field.

kernel/rseq.c

+4 −4
Original line number Diff line number Diff line
@@ -128,10 +128,10 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs) 
	int ret;



#ifdef CONFIG_64BIT

	if (get_user(ptr, &t->rseq->rseq_cs.ptr64))

	if (get_user(ptr, &t->rseq->rseq_cs))

		return -EFAULT;

#else

	if (copy_from_user(&ptr, &t->rseq->rseq_cs.ptr64, sizeof(ptr)))

	if (copy_from_user(&ptr, &t->rseq->rseq_cs, sizeof(ptr)))

		return -EFAULT;

#endif

	if (!ptr) {
@@ -217,9 +217,9 @@ static int clear_rseq_cs(struct task_struct *t) 
	 * Set rseq_cs to NULL.

	 */

#ifdef CONFIG_64BIT

	return put_user(0UL, &t->rseq->rseq_cs.ptr64);

	return put_user(0UL, &t->rseq->rseq_cs);

#else

	if (clear_user(&t->rseq->rseq_cs.ptr64, sizeof(t->rseq->rseq_cs.ptr64)))

	if (clear_user(&t->rseq->rseq_cs, sizeof(t->rseq->rseq_cs)))

		return -EFAULT;

	return 0;

#endif