From: Catalin Marinas <catalin.marinas@arm.com>
To: Andrei Vagin <avagin@gmail.com>
Cc: Will Deacon <will@kernel.org>, Oleg Nesterov <oleg@redhat.com>,
linux-arm-kernel@lists.infradead.org,
LKML <linux-kernel@vger.kernel.org>,
Dave Martin <Dave.Martin@arm.com>,
Keno Fischer <keno@juliacomputing.com>
Subject: Re: [PATCH 1/4] arm64: expose orig_x0 in the user_pt_regs structure
Date: Sat, 27 Mar 2021 13:01:01 +0000 [thread overview]
Message-ID: <20210327130100.GA31076@arm.com> (raw)
In-Reply-To: <CANaxB-xTrMkJ2D19wwjSbCfizdRDnNO52fibpaRXP5g3hOcQwQ@mail.gmail.com>
On Fri, Mar 26, 2021 at 05:35:19PM -0700, Andrei Vagin wrote:
> On Fri, Mar 26, 2021 at 11:28 AM Catalin Marinas
> <catalin.marinas@arm.com> wrote:
> >
> > On Mon, Mar 22, 2021 at 03:50:50PM -0700, Andrei Vagin wrote:
> > > diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
> > > index 758ae984ff97..3c118c5b0893 100644
> > > --- a/arch/arm64/include/uapi/asm/ptrace.h
> > > +++ b/arch/arm64/include/uapi/asm/ptrace.h
> > > @@ -90,6 +90,7 @@ struct user_pt_regs {
> > > __u64 sp;
> > > __u64 pc;
> > > __u64 pstate;
> > > + __u64 orig_x0;
> > > };
> >
> > That's a UAPI change, likely to go wrong. For example, a
> > ptrace(PTRACE_GETREGSET, pid, REGSET_GPR, data) would write past the end
> > of an old struct user_pt_regs in the debugger.
>
> ptrace(PTRACE_GETREGSET, ...) receives iovec:
> ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov)
>
> iov contains a pointer to a buffer and its size and the kernel fills
> only the part that fits the buffer.
> I think this interface was invented to allow extending structures
> without breaking backward compatibility.
You are right here, it doesn't write past the end of the iov buffer.
However, it's still an ABI change. An unaware program using a newer
user_pt_regs but running on an older kernel may be surprised that the
updated iov.len is smaller than sizeof (struct user_pt_regs).
Changing this structure also changes the core dump format, see ELF_NGREG
and ELF_CORE_COPY_REGS. Maybe this doesn't matter much either since the
ELF note would have size information but I'd prefer if we didn't modify
this structure.
--
Catalin
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-03-27 13:03 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-22 22:50 [PATCH 0/4 v3] arm64/ptrace: allow to get all registers on syscall traps Andrei Vagin
2021-03-22 22:50 ` [PATCH 1/4] arm64: expose orig_x0 in the user_pt_regs structure Andrei Vagin
2021-03-26 18:28 ` Catalin Marinas
2021-03-27 0:35 ` Andrei Vagin
2021-03-27 13:01 ` Catalin Marinas [this message]
2021-03-22 22:50 ` [PATCH 2/4] arm64/ptrace: introduce orig_x7 " Andrei Vagin
2021-03-26 18:39 ` Catalin Marinas
2021-03-22 22:50 ` [PATCH 3/4] selftest/arm64/ptrace: add a test for orig_x0 Andrei Vagin
2021-03-22 22:50 ` [PATCH 4/4] selftest/arm64/ptrace: add a test for orig_x7 Andrei Vagin
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=20210327130100.GA31076@arm.com \
--to=catalin.marinas@arm.com \
--cc=Dave.Martin@arm.com \
--cc=avagin@gmail.com \
--cc=keno@juliacomputing.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=oleg@redhat.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
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;
as well as URLs for NNTP newsgroup(s).