Re: [PATCH v2] powerpc/uprobes: Validation for prefixed instruction

[Ravi Bangoria]

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