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Subject: Re: [PATCH v2] powerpc/uprobes: Validation for prefixed instruction
To:     mpe@ellerman.id.au
Cc:     oleg@redhat.com, rostedt@goodmis.org, paulus@samba.org,
        jniethe5@gmail.com, naveen.n.rao@linux.ibm.com,
        sandipan@linux.ibm.com, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org,
        Ravi Bangoria <ravi.bangoria@linux.ibm.com>
References: <20210204104703.273429-1-ravi.bangoria@linux.ibm.com>
From:   Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Message-ID: <79b0bed7-8b98-d58d-dc47-644195bbc095@linux.ibm.com>
Date:   Thu, 4 Feb 2021 16:19:40 +0530
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On 2/4/21 4:17 PM, Ravi Bangoria wrote:
> Don't allow Uprobe on 2nd word of a prefixed instruction. As per
> ISA 3.1, prefixed instruction should not cross 64-byte boundary.
> So don't allow Uprobe on such prefixed instruction as well.
> 
> 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 we notice
> that probe is on the 2nd word of 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.

@mpe,

arch_uprobe_analyze_insn() can return early if
cpu_has_feature(CPU_FTR_ARCH_31) is not set. But that will
miss out a rare scenario of user running binary with prefixed
instruction on p10 predecessors. Please let me know if I
should add cpu_has_feature(CPU_FTR_ARCH_31) or not.

- Ravi