[PATCH v2 01/10] ARM: p2v: fix handling of LPAE translation in BE mode

[Russell King - ARM Linux admin]

On Mon, Sep 21, 2020 at 05:41:08PM +0200, Ard Biesheuvel wrote:
> When running in BE mode on LPAE hardware with a PA-to-VA translation
> that exceeds 4 GB, we patch bits 39:32 of the offset into the wrong
> byte of the opcode. So fix that, by rotating the offset in r0 to the
> right by 8 bits, which will put the 8-bit immediate in bits 31:24.
> 
> Note that this will also move bit #22 in its correct place when
> applying the rotation to the constant #0x400000.
> 
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>

Should this have a fixes tag?

> ---
>  arch/arm/kernel/head.S | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index f8904227e7fd..98c1e68bdfcb 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -671,12 +671,8 @@ ARM_BE8(rev16	ip, ip)
>  	ldrcc	r7, [r4], #4	@ use branch for delay slot
>  	bcc	1b
>  	bx	lr
> -#else
> -#ifdef CONFIG_CPU_ENDIAN_BE8
> -	moveq	r0, #0x00004000	@ set bit 22, mov to mvn instruction
>  #else
>  	moveq	r0, #0x400000	@ set bit 22, mov to mvn instruction
> -#endif
>  	b	2f
>  1:	ldr	ip, [r7, r3]
>  #ifdef CONFIG_CPU_ENDIAN_BE8
> @@ -685,7 +681,7 @@ ARM_BE8(rev16	ip, ip)
>  	tst	ip, #0x000f0000	@ check the rotation field
>  	orrne	ip, ip, r6, lsl #24 @ mask in offset bits 31-24
>  	biceq	ip, ip, #0x00004000 @ clear bit 22
> -	orreq	ip, ip, r0      @ mask in offset bits 7-0
> +	orreq	ip, ip, r0, ror #8  @ mask in offset bits 7-0
>  #else
>  	bic	ip, ip, #0x000000ff
>  	tst	ip, #0xf00	@ check the rotation field
> -- 
> 2.17.1
> 
> 

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