Linux-EFI Archive on lore.kernel.org
 help / color / Atom feed
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
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.

  reply index

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

Linux-EFI Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-efi/0 linux-efi/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-efi linux-efi/ https://lore.kernel.org/linux-efi \
		linux-efi@vger.kernel.org
	public-inbox-index linux-efi

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-efi


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git