Subject: Re: [PATCH v4] powerpc/uprobes: Validation for prefixed instruction

From: Michael Ellerman <[email-masked]>
Date: Tue, 09 Mar 2021 20:54:45 +1100

Ravi Bangoria <[email-masked]> writes:
> As per ISA 3.1, prefixed instruction should not cross 64-byte
> boundary. So don't allow Uprobe on such prefixed instruction.
>
> There are two ways probed instruction is changed in mapped pages.
> First, when Uprobe is activated, it searches for all the relevant
> pages and replace instruction in them. In this case, if that probe
> is on the 64-byte unaligned prefixed instruction, error out
> directly. Second, when Uprobe is already active and user maps a
> relevant page via mmap(), instruction is replaced via mmap() code
> path. But because Uprobe is invalid, entire mmap() operation can
> not be stopped. In this case just print an error and continue.
>
> Signed-off-by: Ravi Bangoria <[email-masked]>
> Acked-by: Naveen N. Rao <[email-masked]>

Do we have a Fixes: tag for this?

> ---
> v3: https://lore.kernel.org/r/[email-masked]
> v3->v4:
>   - CONFIG_PPC64 check was not required, remove it.
>   - Use SZ_ macros instead of hardcoded numbers.
>
>  arch/powerpc/kernel/uprobes.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
> index e8a63713e655..4cbfff6e94a3 100644
> --- a/arch/powerpc/kernel/uprobes.c
> +++ b/arch/powerpc/kernel/uprobes.c
> @@ -41,6 +41,13 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
>  	if (addr & 0x03)
>  		return -EINVAL;
>  
> +	if (cpu_has_feature(CPU_FTR_ARCH_31) &&
> +	    ppc_inst_prefixed(auprobe->insn) &&
> +	    (addr & (SZ_64 - 4)) == SZ_64 - 4) {
> +		pr_info_ratelimited("Cannot register a uprobe on 64 byte unaligned prefixed instruction\n");
> +		return -EINVAL;

I realise we already did the 0x03 check above, but I still think this
would be clearer simply as:

	    (addr & 0x3f == 60)

cheers