From: Willy Tarreau <w@1wt.eu>
To: Borislav Petkov <bp@alien8.de>
Cc: Ammar Faizi <ammar.faizi@students.amikom.ac.id>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Michael Matz <matz@suse.de>
Subject: Re: [PATCH] tools/nolibc: x86: Remove `r8`, `r9` and `r10` from the clobber list
Date: Wed, 13 Oct 2021 16:24:33 +0200 [thread overview]
Message-ID: <20211013142433.GB8557@1wt.eu> (raw)
In-Reply-To: <YWbrR1BqI1CxneN/@zn.tnic>
On Wed, Oct 13, 2021 at 04:20:55PM +0200, Borislav Petkov wrote:
> On Wed, Oct 13, 2021 at 04:07:23PM +0200, Willy Tarreau wrote:
> > Yes I agree with the "potentially" here. If it can potentially be (i.e.
> > the kernel is allowed by contract to later change the way it's currently
> > done) then we have to save them even if it means lower code efficiency.
> >
> > If, however, the kernel performs such savings on purpose because it is
> > willing to observe a stricter saving than the AMD64 ABI, we can follow
> > it but only once it's written down somewhere that it is by contract and
> > will not change.
>
> Right, and Micha noted that such a change to the document can be done.
great.
> And we're basically doing that registers restoring anyway, in POP_REGS.
That's what I based my analysis on when I wanted to verify Ammar's
finding. I would tend to think that if we're burning cycles popping
plenty of registers it's probably for a reason, maybe at least a good
one, which is that it's the only way to make sure we're not leaking
internal kernel data! This is not a concern for kernel->kernel nor
user->user calls but for user->kernel calls it definitely is one, and
I don't think we could relax that series of pop without causing leaks
anyway.
Willy
next prev parent reply other threads:[~2021-10-13 14:24 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-11 4:03 [PATCH] tools/nolibc: x86: Remove `r8`, `r9` and `r10` from the clobber list Ammar Faizi
2021-10-12 5:28 ` Willy Tarreau
2021-10-12 8:36 ` Ammar Faizi
2021-10-12 9:06 ` Willy Tarreau
2021-10-12 20:29 ` Borislav Petkov
2021-10-12 21:51 ` Borislav Petkov
2021-10-12 22:23 ` Ammar Faizi
2021-10-13 3:01 ` Willy Tarreau
2021-10-13 3:32 ` Ammar Faizi
2021-10-13 3:34 ` Ammar Faizi
2021-10-13 3:37 ` Ammar Faizi
2021-10-13 12:43 ` Borislav Petkov
2021-10-13 12:51 ` Willy Tarreau
2021-10-13 13:06 ` Borislav Petkov
2021-10-13 14:07 ` Willy Tarreau
2021-10-13 14:20 ` Borislav Petkov
2021-10-13 14:24 ` Willy Tarreau [this message]
2021-10-13 16:24 ` Michael Matz
2021-10-13 16:30 ` Willy Tarreau
2021-10-13 16:51 ` Andy Lutomirski
2021-10-13 16:52 ` Borislav Petkov
2021-10-14 8:44 ` Ammar Faizi
2021-10-14 12:44 ` Michael Matz
2021-10-14 14:31 ` Borislav Petkov
2021-10-19 9:06 ` David Laight
2021-10-23 20:40 ` H. Peter Anvin
2021-10-12 21:21 ` David Laight
2021-10-12 23:02 ` Subject: " Ammar Faizi
2021-10-13 9:03 ` [PATCH v2] " Ammar Faizi
2021-10-15 8:25 ` [PATCH 0/2] Fix clobber list and startup code bug Ammar Faizi
2021-10-15 8:25 ` [PATCH 1/2] tools/nolibc: x86: Remove `r8`, `r9` and `r10` from the clobber list Ammar Faizi
2021-10-18 5:52 ` Willy Tarreau
2021-10-15 8:25 ` [PATCH 2/2] tools/nolibc: x86-64: Fix startup code bug Ammar Faizi
2021-10-15 8:57 ` Ammar Faizi
2021-10-15 9:26 ` Bedirhan KURT
2021-10-15 9:58 ` Ammar Faizi
2021-10-15 9:41 ` Louvian Lyndal
2021-10-18 4:58 ` Willy Tarreau
2021-10-18 6:53 ` Ammar Faizi
2021-10-23 13:27 ` Ammar Faizi
2021-10-23 13:43 ` Willy Tarreau
2021-10-24 2:11 ` [PATCHSET v2 0/2] tools/nolibc: Fix startup code bug and small improvement Ammar Faizi
2021-10-24 2:11 ` [PATCH 1/2] tools/nolibc: x86-64: Fix startup code bug Ammar Faizi
2021-10-24 2:11 ` [PATCH 2/2] tools/nolibc: x86-64: Use `mov $60,%eax` instead of `mov $60,%rax` Ammar Faizi
2021-10-24 11:41 ` [PATCHSET v2 0/2] tools/nolibc: Fix startup code bug and small improvement Willy Tarreau
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