On Thu, Jan 27, 2022 at 10:27:20AM -0500, Mathieu Desnoyers wrote:
> 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: ec9c82e03a74 ("rseq: uapi: Declare rseq_cs field as union, update includes")
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Florian Weimer <fw@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: linux-api@xxxxxxxxxxxxxxx
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Cc: Dave Watson <davejwatson@xxxxxx>
> Cc: Paul Turner <pjt@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
> Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
> Cc: Ben Maurer <bmaurer@xxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
> Cc: Joel Fernandes <joelaf@xxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
Looks way cleaner now! Fwiw,
Acked-by: Christian Brauner <brauner@xxxxxxxxxx>
> include/uapi/linux/rseq.h | 20 ++++----------------
> kernel/rseq.c | 8 ++++----
> 2 files changed, 8 insertions(+), 20 deletions(-)
>
> diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
> index 9a402fdb60e9..77ee207623a9 100644
> --- a/include/uapi/linux/rseq.h
> +++ b/include/uapi/linux/rseq.h
> @@ -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.
> diff --git a/kernel/rseq.c b/kernel/rseq.c
> index 6d45ac3dae7f..97ac20b4f738 100644
> --- a/kernel/rseq.c
> +++ b/kernel/rseq.c
> @@ -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
> --
> 2.17.1
>
