linux-kernel - Re: [PATCH v2 7/7] arm64: uprobes

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Message-ID: <89110505-da2e-3266-c2aa-6e5128c520a4@arm.com>
Date:   Thu, 27 Sep 2018 18:01:31 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Maciej Slodczyk <m.slodczyk2@...tner.samsung.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     b.zolnierkie@...sung.com, peterz@...radead.org,
        catalin.marinas@....com, will.deacon@....com,
        linux@...linux.org.uk, acme@...nel.org, oleg@...hat.com,
        alexander.shishkin@...ux.intel.com, mingo@...hat.com,
        k.lewandowsk@...sung.com, namhyung@...nel.org, jolsa@...hat.com,
        m.szyprowski@...sung.com
Subject: Re: [PATCH v2 7/7] arm64: uprobes - ARM32 instruction probing

On 26/09/18 13:12, Maciej Slodczyk wrote:
[...]
> @@ -38,16 +78,44 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
>   		unsigned long addr)
>   {
>   	probes_opcode_t insn;
> +	enum probes_insn retval;
> +	unsigned int bpinsn;
>   
> -	/* TODO: Currently we do not support AARCH32 instruction probing */
> -	if (mm->context.flags & MMCF_AARCH32)
> -		return -ENOTSUPP;
> -	else if (!IS_ALIGNED(addr, AARCH64_INSN_SIZE))
> +	insn = *(probes_opcode_t *)(&auprobe->insn[0]);
> +
> +	if (!IS_ALIGNED(addr, AARCH64_INSN_SIZE))
>   		return -EINVAL;
>   
> -	insn = *(probes_opcode_t *)(&auprobe->insn[0]);
> +	/* check if AARCH32 */
> +	if (is_compat_task()) {
> +
> +		/* Thumb is not supported yet */
> +		if (addr & 0x3)

I'm only skimming, so forgive me if I'm missing something which should 
be obvious, but this has a big red flag all over it. If "addr" is the 
actual instruction address (or even a branch target, for a 
non-interworking branch), plenty of Thumb instructions will just happen 
to lie at 4-byte-aligned addresses anyway.

Furthermore, how would this check ever catch anything anyway given 
!IS_ALIGNED(addr, AARCH64_INSN_SIZE) above?

Robin.