Messages in this thread | | | Subject | Re: [PATCH v4] powerpc/uprobes: Validation for prefixed instruction | From | Ravi Bangoria <> | Date | Tue, 9 Mar 2021 18:28:01 +0530 |
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On 3/9/21 4:51 PM, Naveen N. Rao wrote: > On 2021/03/09 08:54PM, Michael Ellerman wrote: >> Ravi Bangoria <ravi.bangoria@linux.ibm.com> writes: >>> As per ISA 3.1, prefixed instruction should not cross 64-byte >>> boundary. So don't allow Uprobe on such prefixed instruction. >>> >>> 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 that probe >>> is on the 64-byte unaligned 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. >>> >>> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com> >>> Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> >> >> Do we have a Fixes: tag for this? > > Since this is an additional check we are adding, I don't think we should > add a Fixes: tag. Nothing is broken per-se -- we're just adding more > checks to catch simple mistakes. Also, like Oleg pointed out, there are > still many other ways for users to shoot themselves in the foot with > uprobes and prefixed instructions, if they so desire. > > However, if you still think we should add a Fixes: tag, we can perhaps > use the below commit since I didn't see any specific commit adding > support for prefixed instructions for uprobes: > > Fixes: 650b55b707fdfa ("powerpc: Add prefixed instructions to > instruction data type")
True. IMO, It doesn't really need any Fixes tag.
> >> >>> --- >>> v3: https://lore.kernel.org/r/20210304050529.59391-1-ravi.bangoria@linux.ibm.com >>> v3->v4: >>> - CONFIG_PPC64 check was not required, remove it. >>> - Use SZ_ macros instead of hardcoded numbers. >>> >>> arch/powerpc/kernel/uprobes.c | 7 +++++++ >>> 1 file changed, 7 insertions(+) >>> >>> diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c >>> index e8a63713e655..4cbfff6e94a3 100644 >>> --- a/arch/powerpc/kernel/uprobes.c >>> +++ b/arch/powerpc/kernel/uprobes.c >>> @@ -41,6 +41,13 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, >>> if (addr & 0x03) >>> return -EINVAL; >>> >>> + if (cpu_has_feature(CPU_FTR_ARCH_31) && >>> + ppc_inst_prefixed(auprobe->insn) && >>> + (addr & (SZ_64 - 4)) == SZ_64 - 4) { >>> + pr_info_ratelimited("Cannot register a uprobe on 64 byte unaligned prefixed instruction\n"); >>> + return -EINVAL; >> >> I realise we already did the 0x03 check above, but I still think this >> would be clearer simply as: >> >> (addr & 0x3f == 60) > > Indeed, I like the use of `60' there -- hex is overrated ;)
Sure. Will resend.
Ravi
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