linux-kernel - Re: [PATCH 1/3] arm64: kprobes: Move extable address check into arch_prepare

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Message-ID: <aec51c10-d744-df0f-1216-d3372e779cb1@arm.com>
Date:   Thu, 3 Jan 2019 17:05:18 +0000
From:   James Morse <james.morse@....com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Pratyush Anand <panand@...hat.com>,
        "David A . Long" <dave.long@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] arm64: kprobes: Move extable address check into
 arch_prepare_kprobe()

Hi!

On 17/12/2018 06:40, Masami Hiramatsu wrote:
> Move extable address check into arch_prepare_kprobe() from
> arch_within_kprobe_blacklist().

I'm trying to work out the pattern for what should go in the blacklist, and what
should be rejected by the arch code.

It seems address-ranges should be blacklisted as the contents don't matter.
easy-example: the idmap text.

The arch code should also reject instructions that can't be probed from
arch_prepare_kprobe(). easy-example: exclusive load or store.


> Please do not blacklisting instructions on exception_table,
> since it is a kind of architectural unsupported instruction.

This doesn't fit the pattern, ... what should it be?

The instructions in the exception_table don't matter, its the address that
indicates there is a fixup for page-faults that occur here. We don't need to
look at the instruction to determine this, why can't we treated these as a
blacklisted range?


Thanks,

James


> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index 2a5b338b2542..b2d4b7428ebc 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -102,6 +102,10 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>  
>  	if (in_exception_text(probe_addr))
>  		return -EINVAL;
> +
> +	if (search_exception_tables(probe_addr))
> +		return -EINVAL;
> +
>  	if (probe_addr >= (unsigned long) __start_rodata &&
>  	    probe_addr <= (unsigned long) __end_rodata)
>  		return -EINVAL;
> @@ -477,8 +481,7 @@ bool arch_within_kprobe_blacklist(unsigned long addr)
>  	    (addr >= (unsigned long)__entry_text_start &&
>  	    addr < (unsigned long)__entry_text_end) ||
>  	    (addr >= (unsigned long)__idmap_text_start &&
> -	    addr < (unsigned long)__idmap_text_end) ||
> -	    !!search_exception_tables(addr))
> +	    addr < (unsigned long)__idmap_text_end))
>  		return true;
>  
>  	if (!is_kernel_in_hyp_mode()) {
>