From: Arvind Sankar <nivedita@alum.mit.edu>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
Dave Young <dyoung@redhat.com>,
pjones@redhat.com, daniel.kiper@oracle.com,
Leif Lindholm <leif@nuviainc.com>, Borislav Petkov <bp@alien8.de>,
Sergey Shatunov <me@prok.pw>,
hpa@zytor.com,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
mingo@redhat.com, Thomas Gleixner <tglx@linutronix.de>,
X86 ML <x86@kernel.org>, linux-efi <linux-efi@vger.kernel.org>,
initramfs@vger.kernel.org,
Donovan Tremura <neurognostic@protonmail.ch>,
Harald Hoyer <harald@hoyer.xyz>
Subject: Re: [PATCH 1/2] efi/x86: Move efi stub globals from .bss to .data
Date: Thu, 9 Apr 2020 12:35:30 -0400 [thread overview]
Message-ID: <20200409163530.GA785575@rani.riverdale.lan> (raw)
In-Reply-To: <CAMj1kXEm=E6B+kjZktG=sBPLQ=_HFfUz6KFLskNGzRnuMjn0gA@mail.gmail.com>
On Thu, Apr 09, 2020 at 04:47:55PM +0200, Ard Biesheuvel wrote:
> On Thu, 9 Apr 2020 at 16:39, Arvind Sankar <nivedita@alum.mit.edu> wrote:
> >
> > On Wed, Apr 08, 2020 at 09:49:15AM +0200, Ard Biesheuvel wrote:
> > > (add Peter, Leif and Daniel)
> > >
> > > On Wed, 8 Apr 2020 at 09:43, Dave Young <dyoung@redhat.com> wrote:
> > > >
> > > > On 04/06/20 at 02:06pm, Arvind Sankar wrote:
> > > > > Commit
> > > > >
> > > > > 3ee372ccce4d ("x86/boot/compressed/64: Remove .bss/.pgtable from
> > > > > bzImage")
> > > > >
> > > > > removed the .bss section from the bzImage.
> > > > >
> > > > > However, while a PE loader is required to zero-initialize the .bss
> > > > > section before calling the PE entry point, the EFI handover protocol
> > > > > does not currently document any requirement that .bss be initialized by
> > > > > the bootloader prior to calling the handover entry.
> > > > >
> > > > > When systemd-boot is used to boot a unified kernel image [1], the image
> > > > > is constructed by embedding the bzImage as a .linux section in a PE
> > > > > executable that contains a small stub loader from systemd together with
> > > > > additional sections and potentially an initrd. As the .bss section
> > > > > within the bzImage is no longer explicitly present as part of the file,
> > > > > it is not initialized before calling the EFI handover entry.
> > > > > Furthermore, as the size of the embedded .linux section is only the size
> > > > > of the bzImage file itself, the .bss section's memory may not even have
> > > > > been allocated.
> > > >
> > > > I did not follow up the old report, maybe I missed something. But not
> > > > sure why only systemd-boot is mentioned here. I also have similar issue
> > > > with early efi failure. With these two patches applied, it works well
> > > > then.
> > > >
> > > > BTW, I use Fedora 31 + Grub2
> > > >
> > >
> > > OK, so I take it this means that GRUB's PE/COFF loader does not
> > > zero-initialize BSS either? Does it honor the image size in memory if
> > > it exceeds the file size?
> >
> > Dave, that comment was because the previous report was for systemd-boot
> > stub.
> >
> > Ard, should I revise the commit message to make it clear it's not
> > restricted to systemd-boot but anything using handover entry may be
> > affected? Maybe just a "for example, when systemd-boot..." and then a
> > line to say grub2 with the EFI stub patches is also impacted?
> >
>
> Well, the fact the /some/ piece of software is used in production that
> relies on the ill-defined EFI handover protocol is sufficient
> justification, so I don't think it is hugely important to update it.
>
> > https://src.fedoraproject.org/rpms/grub2/blob/f31/f/0001-Add-support-for-Linux-EFI-stub-loading.patch#_743
> >
> > + kernel_mem = grub_efi_allocate_pages_max(lh.pref_address,
> > + BYTES_TO_PAGES(lh.init_size));
> >
> > Looking at this, grub does allocate init_size for the image, but it
> > doesn't zero it out.
> >
> > This call also looks wrong to me though. It allocates at max address of
> > pref_address, which, if it succeeds, will guarantee that the kernel gets
> > loaded entirely below pref_address == LOAD_PHYSICAL_ADDR. In native
> > mode, if it weren't for the EFI stub copying the kernel again, this
> > would cause the startup code to relocate the kernel into unallocated
> > memory. On a mixed-mode boot, this would cause the early page tables
> > setup prior to transitioning to 64-bit mode to be in unallocated memory
> > and potentially get clobbered by the EFI stub.
> >
> > The first try to allocate pref_address should be calling
> > grub_efi_allocate_fixed instead.
>
> Thanks Arvind. I'm sure the Fedora/RedHat folks on cc should be able
> to get these logged somewhere.
Ok. For dracut, the process for building the unified kernel image needs
a check to make sure the kernel can fit in the space provided for it --
there is 16MiB of space and the distro bzImage's are up to 10-11MiB in
size, so there's some slack left at present.
Additionally, in mixed-mode, the unified kernel images are quite likely
to end up with early pgtables from startup_32 clobbering the initrd,
independently of the recent kernel changes. Hopefully no-one actually
uses these in mixed-mode.
next prev parent reply other threads:[~2020-04-09 16:35 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200109150218.16544-1-nivedita@alum.mit.edu>
[not found] ` <20200405154245.11972-1-me@prok.pw>
2020-04-05 23:18 ` [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable from bzImage Arvind Sankar
2020-04-06 0:00 ` Sergey Shatunov
2020-04-06 3:51 ` Arvind Sankar
2020-04-06 7:32 ` Ard Biesheuvel
2020-04-06 8:47 ` Borislav Petkov
2020-04-06 9:11 ` Ard Biesheuvel
2020-04-06 11:20 ` Borislav Petkov
2020-04-06 13:22 ` Arvind Sankar
2020-04-06 13:29 ` Ard Biesheuvel
2020-04-06 16:01 ` Arvind Sankar
2020-04-06 16:22 ` Ard Biesheuvel
2020-04-06 16:52 ` Arvind Sankar
2020-04-06 16:59 ` Ard Biesheuvel
2020-04-06 18:06 ` [PATCH 1/2] efi/x86: Move efi stub globals from .bss to .data Arvind Sankar
2020-04-06 18:06 ` [PATCH 2/2] efi/x86: Always relocate the kernel for EFI handover entry Arvind Sankar
2020-04-06 18:29 ` [PATCH 1/2] efi/x86: Move efi stub globals from .bss to .data Ard Biesheuvel
2020-04-08 7:43 ` Dave Young
2020-04-08 7:49 ` Ard Biesheuvel
2020-04-09 14:39 ` Arvind Sankar
2020-04-09 14:47 ` Ard Biesheuvel
2020-04-09 16:35 ` Arvind Sankar [this message]
2020-04-10 14:47 ` Arvind Sankar
2020-04-10 15:26 ` Ard Biesheuvel
2020-04-14 14:57 ` Daniel Kiper
2020-04-10 11:26 ` Thomas Meyer
2020-04-10 14:38 ` Arvind Sankar
2020-04-11 8:50 ` Thomas Meyer
2020-04-06 17:21 ` [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable from bzImage Borislav Petkov
2020-04-06 8:44 ` Ard Biesheuvel
2020-04-06 12:36 ` Sergey Shatunov
2020-04-06 13:20 ` Ard Biesheuvel
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