Message-Id: <DALA5WYA04OG.1283TZDOVLBPS@bootlin.com>
Date: Fri, 13 Jun 2025 10:59:28 +0200
From: Alexis Lothoré <alexis.lothore@...tlin.com>
To: "Peter Zijlstra" <peterz@...radead.org>
Cc: "Alexei Starovoitov" <ast@...nel.org>, "Daniel Borkmann"
 <daniel@...earbox.net>, "Andrii Nakryiko" <andrii@...nel.org>, "Martin
 KaFai Lau" <martin.lau@...ux.dev>, "Eduard Zingerman" <eddyz87@...il.com>,
 "Song Liu" <song@...nel.org>, "Yonghong Song" <yonghong.song@...ux.dev>,
 "John Fastabend" <john.fastabend@...il.com>, "KP Singh"
 <kpsingh@...nel.org>, "Stanislav Fomichev" <sdf@...ichev.me>, "Hao Luo"
 <haoluo@...gle.com>, "Jiri Olsa" <jolsa@...nel.org>, "David S. Miller"
 <davem@...emloft.net>, "David Ahern" <dsahern@...nel.org>, "Thomas
 Gleixner" <tglx@...utronix.de>, "Ingo Molnar" <mingo@...hat.com>, "Borislav
 Petkov" <bp@...en8.de>, "Dave Hansen" <dave.hansen@...ux.intel.com>,
 <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, "Menglong Dong"
 <imagedong@...cent.com>, Björn Töpel
 <bjorn@...nel.org>, "Pu Lehui" <pulehui@...wei.com>, "Puranjay Mohan"
 <puranjay@...nel.org>, "Paul Walmsley" <paul.walmsley@...ive.com>, "Palmer
 Dabbelt" <palmer@...belt.com>, "Albert Ou" <aou@...s.berkeley.edu>,
 "Alexandre Ghiti" <alex@...ti.fr>, "Ilya Leoshkevich" <iii@...ux.ibm.com>,
 "Heiko Carstens" <hca@...ux.ibm.com>, "Vasily Gorbik" <gor@...ux.ibm.com>,
 "Alexander Gordeev" <agordeev@...ux.ibm.com>, "Christian Borntraeger"
 <borntraeger@...ux.ibm.com>, "Sven Schnelle" <svens@...ux.ibm.com>, "Hari
 Bathini" <hbathini@...ux.ibm.com>, "Christophe Leroy"
 <christophe.leroy@...roup.eu>, "Naveen N Rao" <naveen@...nel.org>,
 "Madhavan Srinivasan" <maddy@...ux.ibm.com>, "Michael Ellerman"
 <mpe@...erman.id.au>, "Nicholas Piggin" <npiggin@...il.com>, "Mykola
 Lysenko" <mykolal@...com>, "Shuah Khan" <shuah@...nel.org>, "Maxime
 Coquelin" <mcoquelin.stm32@...il.com>, "Alexandre Torgue"
 <alexandre.torgue@...s.st.com>, <ebpf@...uxfoundation.org>, "Thomas
 Petazzoni" <thomas.petazzoni@...tlin.com>, "Bastien Curutchet"
 <bastien.curutchet@...tlin.com>, <netdev@...r.kernel.org>,
 <bpf@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 Björn Töpel <bjorn@...osinc.com>,
 <linux-riscv@...ts.infradead.org>, <linux-s390@...r.kernel.org>,
 <linuxppc-dev@...ts.ozlabs.org>, <linux-kselftest@...r.kernel.org>,
 <linux-stm32@...md-mailman.stormreply.com>,
 <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH bpf 2/7] bpf/x86: prevent trampoline attachment when
 args location on stack is uncertain

On Fri Jun 13, 2025 at 10:32 AM CEST, Peter Zijlstra wrote:
> On Fri, Jun 13, 2025 at 10:26:37AM +0200, Alexis Lothoré wrote:
>> Hi Peter,
>> 
>> On Fri Jun 13, 2025 at 10:11 AM CEST, Peter Zijlstra wrote:
>> > On Fri, Jun 13, 2025 at 09:37:11AM +0200, Alexis Lothoré (eBPF Foundation) wrote:

[...]

>> Maybe my commit wording is not precise enough, but indeed, there's not
>> doubt about whether the struct value is passed on the stack or through a
>> register/a pair of registers. The doubt is rather about the struct location
>> when it is passed _by value_ and _on the stack_: the ABI indeed clearly
>> states that "Structures and unions assume the alignment of their most
>> strictly aligned component" (p.13), but this rule is "silently broken" when
>> a struct has an __attribute__((packed)) or and __attribute__((aligned(X))),
>> and AFAICT this case can not be detected at runtime with current BTF info.
>
> Ah, okay. So it is a failure of BTF. That was indeed not clear.

If I need to respin, I'll rewrite the commit message to include the details
above.

Alexis




-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Powered by blists - more mailing lists