[PATCH 15/18] powerpc/uprobes: Add support for prefixed instructions

[Balamuruhan S]

On Tue, Nov 26, 2019 at 04:21:38PM +1100, Jordan Niethe wrote:
> Uprobes can execute instructions out of line. Increase the size of the
> buffer used  for this so that this works for prefixed instructions. Take
> into account the length of prefixed instructions when fixing up the nip.
> 
> Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
> ---
>  arch/powerpc/include/asm/uprobes.h | 18 ++++++++++++++----
>  arch/powerpc/kernel/uprobes.c      |  4 ++--
>  2 files changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/uprobes.h b/arch/powerpc/include/asm/uprobes.h
> index 2bbdf27d09b5..5b5e8a3d2f55 100644
> --- a/arch/powerpc/include/asm/uprobes.h
> +++ b/arch/powerpc/include/asm/uprobes.h
> @@ -14,18 +14,28 @@
>  
>  typedef ppc_opcode_t uprobe_opcode_t;
>  
> +/*
> + * We have to ensure we have enought space for prefixed instructions, which

minor typo of `enought` and we can have something like below,

s/We have to ensure we have enought/Ensure we have enough

-- Bala

> + * are double the size of a word instruction, i.e. 8 bytes. However,
> + * sometimes it is simpler to treat a prefixed instruction like 2 word
> + * instructions.
> + */
>  #define MAX_UINSN_BYTES		4
> -#define UPROBE_XOL_SLOT_BYTES	(MAX_UINSN_BYTES)
> +#define UPROBE_XOL_SLOT_BYTES	(2 * MAX_UINSN_BYTES)
>  
>  /* The following alias is needed for reference from arch-agnostic code */
>  #define UPROBE_SWBP_INSN	BREAKPOINT_INSTRUCTION
>  #define UPROBE_SWBP_INSN_SIZE	4 /* swbp insn size in bytes */
>  
>  struct arch_uprobe {
> +	 /*
> +	  * Ensure there is enough space for prefixed instructions. Prefixed
> +	  * instructions must not cross 64-byte boundaries.
> +	  */
>  	union {
> -		u32	insn;
> -		u32	ixol;
> -	};
> +		uprobe_opcode_t	insn[2];
> +		uprobe_opcode_t	ixol[2];
> +	} __aligned(64);
>  };
>  
>  struct arch_uprobe_task {
> diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
> index ab1077dc6148..cfcea6946f8b 100644
> --- a/arch/powerpc/kernel/uprobes.c
> +++ b/arch/powerpc/kernel/uprobes.c
> @@ -111,7 +111,7 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  	 * support doesn't exist and have to fix-up the next instruction
>  	 * to be executed.
>  	 */
> -	regs->nip = utask->vaddr + MAX_UINSN_BYTES;
> +	regs->nip = utask->vaddr + ((IS_PREFIX(auprobe->insn[0])) ? 8 : 4);
>  
>  	user_disable_single_step(current);
>  	return 0;
> @@ -173,7 +173,7 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
>  	 * emulate_step() returns 1 if the insn was successfully emulated.
>  	 * For all other cases, we need to single-step in hardware.
>  	 */
> -	ret = emulate_step(regs, auprobe->insn, 0);
> +	ret = emulate_step(regs, auprobe->insn[0], auprobe->insn[1]);
>  	if (ret > 0)
>  		return true;
>  
> -- 
> 2.20.1
>