[v2] xtensa: align: validate access in fast_load_store

[PATCH v2] xtensa: align: validate access in fast_load_store

Posted by Ricky Ringler 1 day ago

access_ok() is used only in user mode and
branches to .Linvalid_instruction on fault.
Kernel mode behavior unchanged.

v2:
- Address Max's feedback
- Fixed formatting
- Added user mode branch

Tested-by: Ricky Ringler <richard.rringler@gmail.com>

Testing:
- Built with CONFIG_MMU enabled
- objdump before/after comparison and validated code path

Signed-off-by: Ricky Ringler <richard.rringler@gmail.com>
---
 arch/xtensa/kernel/align.S | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/xtensa/kernel/align.S b/arch/xtensa/kernel/align.S
index ee97edce2300..64e775933e9b 100644
--- a/arch/xtensa/kernel/align.S
+++ b/arch/xtensa/kernel/align.S
@@ -21,6 +21,9 @@
 #include <asm/asm-offsets.h>
 #include <asm/asmmacro.h>
 #include <asm/processor.h>
+#ifdef CONFIG_MMU
+#include <asm/asm-uaccess.h>
+#endif
 
 #if XCHAL_UNALIGNED_LOAD_EXCEPTION || defined CONFIG_XTENSA_LOAD_STORE
 #define LOAD_EXCEPTION_HANDLER
@@ -185,8 +188,12 @@ ENTRY(fast_load_store)
 
 #ifdef CONFIG_MMU
 	/* l32e can't be used here even when it's available. */
-	/* TODO access_ok(a3) could be used here */
-	j	.Linvalid_instruction
+	rsr	a6, ps
+	bbsi.l	a6, PS_UM_BIT, 1f	# user mode
+	j	.Linvalid_instruction	# kernel mode
+1:
+	movi	a5, 8
+	access_ok a3, a5, a6, a2, .Linvalid_instruction
 #endif
 	l32i	a5, a3, 0
 	l32i	a6, a3, 4
-- 
2.43.0

Re: [PATCH v2] xtensa: align: validate access in fast_load_store

Posted by Max Filippov 19 hours ago

On Sun, Dec 14, 2025 at 2:30 PM Ricky Ringler
<richard.rringler@gmail.com> wrote:
>
> access_ok() is used only in user mode and
> branches to .Linvalid_instruction on fault.
> Kernel mode behavior unchanged.
>
> v2:
> - Address Max's feedback
> - Fixed formatting
> - Added user mode branch

Please move the patch change log past the `---` marker so that
it is dropped when the patch is committed.

> Tested-by: Ricky Ringler <richard.rringler@gmail.com>
>
> Testing:
> - Built with CONFIG_MMU enabled
> - objdump before/after comparison and validated code path
>
> Signed-off-by: Ricky Ringler <richard.rringler@gmail.com>
> ---
>  arch/xtensa/kernel/align.S | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/arch/xtensa/kernel/align.S b/arch/xtensa/kernel/align.S
> index ee97edce2300..64e775933e9b 100644
> --- a/arch/xtensa/kernel/align.S
> +++ b/arch/xtensa/kernel/align.S
> @@ -21,6 +21,9 @@
>  #include <asm/asm-offsets.h>
>  #include <asm/asmmacro.h>
>  #include <asm/processor.h>
> +#ifdef CONFIG_MMU
> +#include <asm/asm-uaccess.h>
> +#endif
>
>  #if XCHAL_UNALIGNED_LOAD_EXCEPTION || defined CONFIG_XTENSA_LOAD_STORE
>  #define LOAD_EXCEPTION_HANDLER
> @@ -185,8 +188,12 @@ ENTRY(fast_load_store)
>
>  #ifdef CONFIG_MMU
>         /* l32e can't be used here even when it's available. */
> -       /* TODO access_ok(a3) could be used here */
> -       j       .Linvalid_instruction
> +       rsr     a6, ps
> +       bbsi.l  a6, PS_UM_BIT, 1f       # user mode
> +       j       .Linvalid_instruction   # kernel mode

It should be the other way around: kernel mode is allowed to access
anything, user mode needs address checking.

> +1:
> +       movi    a5, 8
> +       access_ok a3, a5, a6, a2, .Linvalid_instruction
>  #endif
>         l32i    a5, a3, 0
>         l32i    a6, a3, 4
> --
> 2.43.0
>


-- 
Thanks.
-- Max

[PATCH v3] xtensa: align: validate access in fast_load_store

Posted by Ricky Ringler 7 hours ago

access_ok() is used only in user mode and
branches to .Linvalid_instruction on fault.
Kernel mode skips access_ok().

Tested-by: Ricky Ringler <richard.rringler@gmail.com>

Signed-off-by: Ricky Ringler <richard.rringler@gmail.com>
---
v3:
- Changed kernel mode behavior to skip access_ok()

v2:
- Address Max's feedback
- Fixed formatting
- Added user mode branch

Testing:
- Built with CONFIG_MMU enabled
- objdump before/after comparison and validated code path

 arch/xtensa/kernel/align.S | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/xtensa/kernel/align.S b/arch/xtensa/kernel/align.S
index ee97edce2300..f2d0d831ce43 100644
--- a/arch/xtensa/kernel/align.S
+++ b/arch/xtensa/kernel/align.S
@@ -21,6 +21,9 @@
 #include <asm/asm-offsets.h>
 #include <asm/asmmacro.h>
 #include <asm/processor.h>
+#ifdef CONFIG_MMU
+#include <asm/asm-uaccess.h>
+#endif
 
 #if XCHAL_UNALIGNED_LOAD_EXCEPTION || defined CONFIG_XTENSA_LOAD_STORE
 #define LOAD_EXCEPTION_HANDLER
@@ -185,8 +188,11 @@ ENTRY(fast_load_store)
 
 #ifdef CONFIG_MMU
 	/* l32e can't be used here even when it's available. */
-	/* TODO access_ok(a3) could be used here */
-	j	.Linvalid_instruction
+	rsr	a6, ps
+	bbci.l	a6, PS_UM_BIT, 1f # kernel mode
+	movi	a5, 8
+	access_ok a3, a5, a6, a2, .Linvalid_instruction
+1:
 #endif
 	l32i	a5, a3, 0
 	l32i	a6, a3, 4
-- 
2.43.0

Re: [PATCH v3] xtensa: align: validate access in fast_load_store

Posted by Max Filippov 7 hours ago

On Mon, Dec 15, 2025 at 6:33 AM Ricky Ringler
<richard.rringler@gmail.com> wrote:
>
> access_ok() is used only in user mode and
> branches to .Linvalid_instruction on fault.
> Kernel mode skips access_ok().
>
> Tested-by: Ricky Ringler <richard.rringler@gmail.com>
>
> Signed-off-by: Ricky Ringler <richard.rringler@gmail.com>
> ---
> v3:
> - Changed kernel mode behavior to skip access_ok()
>
> v2:
> - Address Max's feedback
> - Fixed formatting
> - Added user mode branch
>
> Testing:
> - Built with CONFIG_MMU enabled
> - objdump before/after comparison and validated code path
>
>  arch/xtensa/kernel/align.S | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)

Thanks. Applied to my xtensa tree.
-- Max