Subject: [PATCH] ARM: kprobes-decode: add support for MOVW instruction

From: [email-masked] (Will Deacon)
Date: Mon, 27 Sep 2010 14:16:29 +0100

> The MOVW instruction moves a 16-bit immediate into the bottom halfword
> of the destination register.
> 
> This patch ensures that kprobes leaves the 16-bit immediate intact, rather
> than assume a 12-bit immediate and mask out the upper 4 bits.
> 
> Cc: Nicolas Pitre <[email-masked]>
> Signed-off-by: Will Deacon <[email-masked]>
> ---
>  arch/arm/kernel/kprobes-decode.c |    7 ++++---
>  1 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/kernel/kprobes-decode.c b/arch/arm/kernel/kprobes-decode.c
> index 8bccbfa..2c1f005 100644
> --- a/arch/arm/kernel/kprobes-decode.c
> +++ b/arch/arm/kernel/kprobes-decode.c
> @@ -1162,11 +1162,12 @@ space_cccc_001x(kprobe_opcode_t insn, struct arch_specific_insn *asi)
>  {
>  	/*
>  	 * MSR   : cccc 0011 0x10 xxxx xxxx xxxx xxxx xxxx
> -	 * Undef : cccc 0011 0x00 xxxx xxxx xxxx xxxx xxxx
> +	 * Undef : cccc 0011 0100 xxxx xxxx xxxx xxxx xxxx
>  	 * ALU op with S bit and Rd == 15 :
>  	 *	   cccc 001x xxx1 xxxx 1111 xxxx xxxx xxxx
>  	 */
> -	if ((insn & 0x0f900000) == 0x03200000 ||	/* MSR & Undef */
> +	if ((insn & 0x0fb00000) == 0x03200000 ||	/* MSR */
> +	    (insn & 0x0ff00000) == 0x03400000 ||	/* Undef */
>  	    (insn & 0x0e10f000) == 0x0210f000)		/* ALU s-bit, R15  */
>  		return INSN_REJECTED;
> 
> @@ -1177,7 +1178,7 @@ space_cccc_001x(kprobe_opcode_t insn, struct arch_specific_insn *asi)
>  	 * *S (bit 20) updates condition codes
>  	 * ADC/SBC/RSC reads the C flag
>  	 */
> -	insn &= 0xfff00fff;	/* Rn = r0, Rd = r0 */
> +	insn &= 0xffff0fff;	/* Rd = r0 */
>  	asi->insn[0] = insn;
>  	asi->insn_handler = (insn & (1 << 20)) ?  /* S-bit */
>  			emulate_alu_imm_rwflags : emulate_alu_imm_rflags;
> --
> 1.7.0.4

I forgot to mention; without this patch the kprobes smoke tests
(CONFIG_KPROBES_SANITY_TEST) fail on ARM. If nobody objects, I'll
submit this to the patch system this week.

Thanks,

Will