From: Linus Torvalds <torvalds@linux-foundation.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Andi Kleen <ak@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>,
Brian Gerst <brgerst@gmail.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
"the arch/x86 maintainers" <x86@kernel.org>,
Maninder Singh <maninder1.s@samsung.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH 0/3] syscalls: clean up stub naming convention
Date: Mon, 9 Apr 2018 12:13:50 -0700 [thread overview]
Message-ID: <CA+55aFzB1+e+X0pWgNyyQXiU34RnTk8swaqewbzSYK29gu-_dA@mail.gmail.com> (raw)
In-Reply-To: <20180409063921.wkrqbnv4lzxb3isg@gmail.com>
On Sun, Apr 8, 2018 at 11:39 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> I see - so it's _not_ the same function call signature, but a wrapper with a
> sign-extended version, which is fair and useful. So on architectures where this
> matters there's type conversion and active code generated.
Exactly. Some architectures have that as part of their ABI.
On Powerpc, for example, when you pass an "int" argument, the ABI
specifies that you have to sign-extend the register in the caller to
64 bits.
And the generated code actually depends on that behavior, in that
maybe it first tests the 32 bit value, but then _uses_ the full 64
bits, knowing that the caller sign-extended it properly.
This is a problem with the system call interface, since the caller
isn't a trusted entity, and user space could pass an "int" value with
the high bits set to something that _isn't_ the sign-extended thing,
so then the compiler generates unsafe code.
On x86, this never happens, since x86 doesn't have that "hidden higher
bits matter" ABI model. So that part of the wrapper will be a complete
no-op. But some other architectures depend on it.
Linus
next prev parent reply other threads:[~2018-04-09 19:13 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-07 7:46 [PATCH 0/3] syscalls: clean up stub naming convention Dominik Brodowski
2018-04-07 7:46 ` [PATCH 1/3] syscalls: clean up syscall " Dominik Brodowski
2018-04-07 7:46 ` [PATCH 2/3] syscalls: clean up compat " Dominik Brodowski
2018-04-07 7:46 ` [PATCH 3/3] syscalls: rename struct pt_regs-based sys_*() to __x64_sys_*() Dominik Brodowski
2018-04-08 8:35 ` [PATCH 0/3] syscalls: clean up stub naming convention Ingo Molnar
2018-04-08 9:15 ` Dominik Brodowski
2018-04-08 19:59 ` Dominik Brodowski
2018-04-08 20:06 ` [PATCH 4/3] syscalls/x86: adapt syscall_wrapper.h to the new syscall " Dominik Brodowski
2018-04-09 6:49 ` [PATCH 0/3] syscalls: clean up " Ingo Molnar
2018-04-09 6:54 ` Dominik Brodowski
2018-04-09 6:39 ` Ingo Molnar
2018-04-09 19:13 ` Linus Torvalds [this message]
2018-04-09 6:45 ` Ingo Molnar
2018-04-09 6:53 ` Dominik Brodowski
2018-04-09 7:06 ` Ingo Molnar
2018-04-09 7:08 ` Dominik Brodowski
2018-04-09 7:34 ` Ingo Molnar
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=CA+55aFzB1+e+X0pWgNyyQXiU34RnTk8swaqewbzSYK29gu-_dA@mail.gmail.com \
--to=torvalds@linux-foundation.org \
--cc=ak@linux.intel.com \
--cc=akpm@linux-foundation.org \
--cc=arnd@arndb.de \
--cc=brgerst@gmail.com \
--cc=dvlasenk@redhat.com \
--cc=hpa@zytor.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@dominikbrodowski.net \
--cc=luto@kernel.org \
--cc=maninder1.s@samsung.com \
--cc=mingo@kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=viro@zeniv.linux.org.uk \
--cc=x86@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).