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

From: Ravi Bangoria
Date: Thu Feb 04 2021 - 05:51:19 EST




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