From: Arvind Sankar <nivedita@alum.mit.edu>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Ard Biesheuvel <ardb@kernel.org>,
linux-efi <linux-efi@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/7] efi/x86: Don't depend on firmware GDT layout
Date: Sun, 2 Feb 2020 13:18:53 -0500 [thread overview]
Message-ID: <20200202181853.GA3798718@rani.riverdale.lan> (raw)
In-Reply-To: <CAKv+Gu9_bXmRMqs3Es7XXFjRafAm0HjyM6EasuKP1nka-dLdVA@mail.gmail.com>
On Sun, Feb 02, 2020 at 06:54:48PM +0100, Ard Biesheuvel wrote:
> On Sun, 2 Feb 2020 at 18:13, Arvind Sankar <nivedita@alum.mit.edu> wrote:
> >
> > At handover entry in efi32_stub_entry, the firmware's GDT is still
> > installed. We save the GDTR for later use in __efi64_thunk but we are
> > assuming that descriptor 2 (__KERNEL_CS) is a valid 32-bit code segment
> > descriptor and that descriptor 3 (__KERNEL_DS/__BOOT_DS) is a valid data
> > segment descriptor.
> >
> > This happens to be true for OVMF (it actually uses descriptor 1 for data
> > segments, but descriptor 3 is also setup as data), but we shouldn't
> > depend on this being the case.
> >
> > Fix this by saving the code and data selectors in addition to the GDTR
> > in efi32_stub_entry, and restoring them in __efi64_thunk before calling
> > the firmware. The UEFI specification guarantees that selectors will be
> > flat, so using the DS selector for all the segment registers should be
> > enough.
> >
> > We also need to install our own GDT before initializing segment
> > registers in startup_32, so move the GDT load up to the beginning of the
> > function.
> >
> > Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
>
> It might be useful to mention /somewhere/ in the commit log that this
> applies to mixed mode
>
Good point. I'll wait for comments from the x86 guys and include that in
the next re-spin.
next prev parent reply other threads:[~2020-02-02 18:18 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-30 20:04 [PATCH 0/8] Remove 64-bit GDT setup in efi_main + doc fixes Arvind Sankar
2020-01-30 20:04 ` [PATCH 1/8] efi/x86: Use C wrapper instead of inline assembly Arvind Sankar
2020-01-30 20:04 ` [PATCH 2/8] efi/x86: Allocate the GDT pointer on the stack Arvind Sankar
2020-01-30 20:04 ` [PATCH 3/8] efi/x86: Factor GDT setup code into a function Arvind Sankar
2020-01-30 20:04 ` [PATCH 4/8] efi/x86: Only setup the GDT for 32-bit kernel Arvind Sankar
2020-01-30 20:04 ` [PATCH 5/8] efi/x86: Allocate only the required 32 bytes for the GDT Arvind Sankar
2020-01-30 20:04 ` [PATCH 6/8] efi/x86: Change __KERNEL_{CS,DS} to __BOOT_{CS,DS} Arvind Sankar
2020-01-30 20:04 ` [PATCH 7/8] Documentation/x86/boot: Clarify segment requirements for EFI handover Arvind Sankar
2020-01-31 19:24 ` Arvind Sankar
2020-01-30 20:04 ` [PATCH 8/8] Documentation/x86/boot: Correct segment requirements for 64-bit boot Arvind Sankar
2020-01-31 8:42 ` [PATCH 0/8] Remove 64-bit GDT setup in efi_main + doc fixes Ard Biesheuvel
2020-01-31 9:31 ` Ard Biesheuvel
2020-01-31 19:10 ` Arvind Sankar
2020-02-02 17:13 ` [PATCH v2 0/7] x86/efi,boot: GDT handling cleanup/fixes Arvind Sankar
2020-02-02 17:13 ` [PATCH v2 1/7] x86/boot: Remove KEEP_SEGMENTS support Arvind Sankar
2020-02-02 17:13 ` [PATCH v2 2/7] efi/x86: Don't depend on firmware GDT layout Arvind Sankar
2020-02-02 17:54 ` Ard Biesheuvel
2020-02-02 18:18 ` Arvind Sankar [this message]
2020-02-02 17:13 ` [PATCH v2 3/7] x86/boot: Reload GDTR after copying to the end of the buffer Arvind Sankar
2020-02-02 17:13 ` [PATCH v2 4/7] x86/boot: Clear direction and interrupt flags in startup_64 Arvind Sankar
2020-02-02 17:13 ` [PATCH v2 5/7] efi/x86: Remove GDT setup from efi_main Arvind Sankar
2020-02-02 17:13 ` [PATCH v2 6/7] x86/boot: GDT limit value should be size - 1 Arvind Sankar
2020-02-02 17:13 ` [PATCH v2 7/7] x86/boot: Micro-optimize GDT loading instructions Arvind Sankar
2020-02-02 18:01 ` [PATCH v2 0/7] x86/efi,boot: GDT handling cleanup/fixes Ard Biesheuvel
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=20200202181853.GA3798718@rani.riverdale.lan \
--to=nivedita@alum.mit.edu \
--cc=ard.biesheuvel@linaro.org \
--cc=ardb@kernel.org \
--cc=bp@alien8.de \
--cc=hpa@zytor.com \
--cc=linux-efi@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=tglx@linutronix.de \
--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).