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.

Mathieu Desnoyers committed 4 years ago

Commit bfdf4e61 parent 5c105d52 files · +8 −20Browse files

Unified · Split

2 files

include/uapi/linux/rseq.h +4 −16
kernel/rseq.c +4 −4

include/uapi/linux/rseq.h+4−16

@@ -105,23 +105,11 @@ struct rseq { · 104 unmodified lines
105	105	* Read and set by the kernel. Set by user-space with single-copy
106	106	* atomicity semantics. This field should only be updated by the
107	107	* thread which registered this data structure. Aligned on 64-bit.
	108	+ *
	109	+ * 32-bit architectures should update the low order bits of the
	110	+ * rseq_cs field, leaving the high order bits initialized to 0.
108	111	*/
109		− union {
110		− __u64 ptr64;
111		−#ifdef __LP64__
112		− __u64 ptr;
113		−#else
114		− struct {
115		−#if (defined(__BYTE_ORDER) && (__BYTE_ORDER == __BIG_ENDIAN)) \|\| defined(__BIG_ENDIAN)
116		− __u32 padding; /* Initialized to zero. */
117		− __u32 ptr32;
118		−#else /* LITTLE */
119		− __u32 ptr32;
120		− __u32 padding; /* Initialized to zero. */
121		−#endif /* ENDIAN */
122		− } ptr;
123		−#endif
124		− } rseq_cs;
	112	+ __u64 rseq_cs;
125	113
126	114	/*
127	115	* Restartable sequences flags field.

kernel/rseq.c+4−4

@@ -128,10 +128,10 @@ static int rseq_get_rseq_cs(struct task_struct t, struct rseq_cs rseq_cs) · 127 unmodified lines
128	128	int ret;
129	129
130	130	#ifdef CONFIG_64BIT
131		− if (get_user(ptr, &t->rseq->rseq_cs.ptr64))
	131	+ if (get_user(ptr, &t->rseq->rseq_cs))
132	132	return -EFAULT;
133	133	#else
134		− if (copy_from_user(&ptr, &t->rseq->rseq_cs.ptr64, sizeof(ptr)))
	134	+ if (copy_from_user(&ptr, &t->rseq->rseq_cs, sizeof(ptr)))
135	135	return -EFAULT;
136	136	#endif
137	137	if (!ptr) {
@@ -217,9 +217,9 @@ static int clear_rseq_cs(struct task_struct *t) · 79 unmodified lines
217	217	* Set rseq_cs to NULL.
218	218	*/
219	219	#ifdef CONFIG_64BIT
220		− return put_user(0UL, &t->rseq->rseq_cs.ptr64);
	220	+ return put_user(0UL, &t->rseq->rseq_cs);
221	221	#else
222		− if (clear_user(&t->rseq->rseq_cs.ptr64, sizeof(t->rseq->rseq_cs.ptr64)))
	222	+ if (clear_user(&t->rseq->rseq_cs, sizeof(t->rseq->rseq_cs)))
223	223	return -EFAULT;
224	224	return 0;
225	225	#endif