From: Michael Ellerman <mpe@ellerman•id.au>
To: Ravi Bangoria <ravi.bangoria@linux•ibm.com>,
"Naveen N. Rao" <naveen.n.rao@linux•vnet.ibm.com>
Cc: Ravi Bangoria <ravi.bangoria@linux•ibm.com>,
jniethe5@gmail•com, oleg@redhat•com, rostedt@goodmis•org,
linux-kernel@vger•kernel.org, paulus@samba•org,
sandipan@linux•ibm.com, naveen.n.rao@linux•ibm.com,
linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH v4] powerpc/uprobes: Validation for prefixed instruction
Date: Wed, 10 Mar 2021 16:13:51 +1100 [thread overview]
Message-ID: <877dmfr3ow.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <1a080cb5-af98-6b6e-352d-772a90cfa902@linux.ibm.com>
Ravi Bangoria <ravi.bangoria@linux•ibm.com> writes:
> 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.
Yep OK, I'm happy without a Fixes tag based on that explanation.
>>>> 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.
Thanks.
cheers
prev parent reply other threads:[~2021-03-10 5:14 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-05 11:54 [PATCH v4] powerpc/uprobes: Validation for prefixed instruction Ravi Bangoria
2021-03-08 4:33 ` Sandipan Das
2021-03-09 9:54 ` Michael Ellerman
2021-03-09 11:21 ` Naveen N. Rao
2021-03-09 12:58 ` Ravi Bangoria
2021-03-10 5:13 ` Michael Ellerman [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=877dmfr3ow.fsf@mpe.ellerman.id.au \
--to=mpe@ellerman$(echo .)id.au \
--cc=jniethe5@gmail$(echo .)com \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=linuxppc-dev@lists$(echo .)ozlabs.org \
--cc=naveen.n.rao@linux$(echo .)ibm.com \
--cc=naveen.n.rao@linux$(echo .)vnet.ibm.com \
--cc=oleg@redhat$(echo .)com \
--cc=paulus@samba$(echo .)org \
--cc=ravi.bangoria@linux$(echo .)ibm.com \
--cc=rostedt@goodmis$(echo .)org \
--cc=sandipan@linux$(echo .)ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox