Re: [RFC PATCH -next V3 4/6] arm64: add copy_{to, from}_user to machine check safe

[Robin Murphy]

On 12/04/2022 8:25 am, Tong Tiangen wrote:
[...]
> diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
> index 0557af834e03..bb17f0829042 100644
> --- a/arch/arm64/include/asm/asm-uaccess.h
> +++ b/arch/arm64/include/asm/asm-uaccess.h
> @@ -92,4 +92,20 @@ alternative_else_nop_endif
>   
>   		_asm_extable	8888b,\l;
>   	.endm
> +
> +	.macro user_ldp_mc l, reg1, reg2, addr, post_inc
> +8888:		ldtr	\reg1, [\addr];
> +8889:		ldtr	\reg2, [\addr, #8];
> +		add	\addr, \addr, \post_inc;
> +
> +		_asm_extable_uaccess_mc	8888b, \l;
> +		_asm_extable_uaccess_mc	8889b, \l;
> +	.endm

You're replacing the only user of this, so please just 
s/_asm_extable/_asm_extable_uaccess_mc/ in the existing macro and save 
the rest of the churn.

Furthermore, how come you're not similarly updating user_stp, given that 
you *are* updating the other stores in copy_to_user?

> +
> +	.macro user_ldst_mc l, inst, reg, addr, post_inc
> +8888:		\inst		\reg, [\addr];
> +		add		\addr, \addr, \post_inc;
> +
> +		_asm_extable_uaccess_mc	8888b, \l;
> +	.endm

Similarly, I think we can just update user_ldst itself. The two 
instances that you're not replacing here are bogus anyway, and deserve 
to be fixed with the patch below first.

[...]
> @@ -62,7 +63,11 @@ SYM_FUNC_START(__arch_copy_from_user)
>   	ret
>   
>   	// Exception fixups
> -9997:	cmp	dst, dstin
> +9997:	mrs esr, esr_el1			// Check exception first
> +	and esr, esr, #ESR_ELx_FSC
> +	cmp esr, #ESR_ELx_FSC_EXTABT

Should we be checking EC to make sure it's a data abort - and thus FSC 
is valid - in the first place? I'm a little fuzzy on all the possible 
paths into fixup_exception(), and it's not entirely obvious whether this 
is actually safe or not.

Thanks,
Robin.

----->8-----
Subject: [PATCH] arm64: mte: Clean up user tag accessors

Invoking user_ldst to explicitly add a post-increment of 0 is silly.
Just use a normal USER() annotation and save the redundant instruction.

Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
---
 arch/arm64/lib/mte.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
index 8590af3c98c0..eeb9e45bcce8 100644
--- a/arch/arm64/lib/mte.S
+++ b/arch/arm64/lib/mte.S
@@ -93,7 +93,7 @@ SYM_FUNC_START(mte_copy_tags_from_user)
 	mov	x3, x1
 	cbz	x2, 2f
 1:
-	user_ldst 2f, ldtrb, w4, x1, 0
+USER(2f, ldtrb	w4, [x1])
 	lsl	x4, x4, #MTE_TAG_SHIFT
 	stg	x4, [x0], #MTE_GRANULE_SIZE
 	add	x1, x1, #1
@@ -120,7 +120,7 @@ SYM_FUNC_START(mte_copy_tags_to_user)
 1:
 	ldg	x4, [x1]
 	ubfx	x4, x4, #MTE_TAG_SHIFT, #MTE_TAG_SIZE
-	user_ldst 2f, sttrb, w4, x0, 0
+USER(2f, sttrb	w4, [x0])
 	add	x0, x0, #1
 	add	x1, x1, #MTE_GRANULE_SIZE
 	subs	x2, x2, #1
--
2.28.0.dirty