[v2] rseq: Remove broken uapi field layout on 32-bit little endian

[RFC PATCH v2] rseq: Remove broken uapi field layout on 32-bit little endian

Posted by Mathieu Desnoyers 4 years, 5 months ago

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@efficios.com>
Cc: Florian Weimer <fw@deneb.enyo.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-api@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Watson <davejwatson@fb.com>
Cc: Paul Turner <pjt@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Ben Maurer <bmaurer@fb.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
---
 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

Re: [RFC PATCH v2] rseq: Remove broken uapi field layout on 32-bit little endian

Posted by Christian Brauner 4 years, 5 months ago

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@efficios.com>
> Cc: Florian Weimer <fw@deneb.enyo.de>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: linux-api@vger.kernel.org
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Dave Watson <davejwatson@fb.com>
> Cc: Paul Turner <pjt@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Russell King <linux@arm.linux.org.uk>
> Cc: "H . Peter Anvin" <hpa@zytor.com>
> Cc: Andi Kleen <andi@firstfloor.org>
> Cc: Christian Brauner <christian.brauner@ubuntu.com>
> Cc: Ben Maurer <bmaurer@fb.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Michael Kerrisk <mtk.manpages@gmail.com>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> ---

Looks way cleaner now! Fwiw,
Acked-by: Christian Brauner <brauner@kernel.org>

>  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
>

[tip: sched/core] rseq: Remove broken uapi field layout on 32-bit little endian

Posted by tip-bot2 for Mathieu Desnoyers 4 years, 4 months ago

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     bfdf4e6208051ed7165b2e92035b4bf11f43eb63
Gitweb:        https://git.kernel.org/tip/bfdf4e6208051ed7165b2e92035b4bf11f43eb63
Author:        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
AuthorDate:    Thu, 27 Jan 2022 10:27:20 -05:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 02 Feb 2022 13:11:34 +01:00

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: ec9c82e03a74 ("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
---
 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 9a402fd..77ee207 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 6d45ac3..97ac20b 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