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

[Ananth N Mavinakayanahalli]

On 2/4/21 4:19 PM, Ravi Bangoria wrote:
> 
> 
> 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.

Wouldn't that binary get a SIGILL in any case? I concur with Naveen...
it makes sense to add the check.


-- 
Ananth