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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: ec9c82e03a ("rseq: uapi: Declare rseq_cs field as union, update includes")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220127152720.25898-1-mathieu.desnoyers@efficios.com
This commit is contained in:
Mathieu Desnoyers 2022-01-27 10:27:20 -05:00 committed by Peter Zijlstra
parent 5c105d55a9
commit bfdf4e6208
2 changed files with 8 additions and 20 deletions
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20
include/uapi/linux/rseq.h
View File

@ -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.

8
kernel/rseq.c
View File

@ -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