From: Brian Gerst <brgerst@gmail.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Arvind Sankar <nivedita@alum.mit.edu>,
Borislav Petkov <bp@suse.de>,
Colin Ian King <colin.king@canonical.com>,
Gary Lin <glin@suse.com>, Jiri Slaby <jslaby@suse.cz>,
Sergey Shatunov <me@prok.pw>, Takashi Iwai <tiwai@suse.de>
Subject: Re: [PATCH 3/9] efi/x86: Move efi stub globals from .bss to .data
Date: Thu, 9 Apr 2020 16:53:07 -0400 [thread overview]
Message-ID: <CAMzpN2jFbf8k99pWaTYRBmSB+iNAKYsufjEhqO6Vv0qxAcHyGA@mail.gmail.com> (raw)
In-Reply-To: <CAMzpN2gJWwVun1Kp6vGuza9LM5KpB=0EwsP8x8eOJQuDGh38Hg@mail.gmail.com>
On Thu, Apr 9, 2020 at 4:05 PM Brian Gerst <brgerst@gmail.com> wrote:
>
> On Thu, Apr 9, 2020 at 9:07 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > From: Arvind Sankar <nivedita@alum.mit.edu>
> >
> > 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.
> >
> > In particular, this can result in efi_disable_pci_dma being true even
> > when it was not specified via the command line or configuration option,
> > which in turn causes crashes while booting on some systems.
> >
> > To avoid issues, place all EFI stub global variables into the .data
> > section instead of .bss. As of this writing, only boolean flags for a
> > few command line arguments and the sys_table pointer were in .bss and
> > will now move into the .data section.
> >
> > [1] https://systemd.io/BOOT_LOADER_SPECIFICATION/#type-2-efi-unified-kernel-images
> >
> > Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
> > Reported-by: Sergey Shatunov <me@prok.pw>
> > Fixes: 3ee372ccce4d ("x86/boot/compressed/64: Remove .bss/.pgtable from bzImage")
> > Link: https://lore.kernel.org/r/20200406180614.429454-1-nivedita@alum.mit.edu
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> > drivers/firmware/efi/libstub/efistub.h | 2 +-
> > drivers/firmware/efi/libstub/x86-stub.c | 2 +-
> > 2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
> > index cc90a748bcf0..67d26949fd26 100644
> > --- a/drivers/firmware/efi/libstub/efistub.h
> > +++ b/drivers/firmware/efi/libstub/efistub.h
> > @@ -25,7 +25,7 @@
> > #define EFI_ALLOC_ALIGN EFI_PAGE_SIZE
> > #endif
> >
> > -#ifdef CONFIG_ARM
> > +#if defined(CONFIG_ARM) || defined(CONFIG_X86)
> > #define __efistub_global __section(.data)
> > #else
> > #define __efistub_global
> > diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
> > index e02ea51273ff..867a57e28980 100644
> > --- a/drivers/firmware/efi/libstub/x86-stub.c
> > +++ b/drivers/firmware/efi/libstub/x86-stub.c
> > @@ -20,7 +20,7 @@
> > /* Maximum physical address for 64-bit kernel with 4-level paging */
> > #define MAXMEM_X86_64_4LEVEL (1ull << 46)
> >
> > -static efi_system_table_t *sys_table;
> > +static efi_system_table_t *sys_table __efistub_global;
> > extern const bool efi_is64;
> > extern u32 image_offset;
> >
> > --
> > 2.17.1
> >
>
> Can we use the -fno-zero-initialized-in-bss compiler flag instead of
> explicitly marking global variables?
Scratch that. Apparently it only works when a variable is explicitly
initialized to zero.
--
Brian Gerst
next prev parent reply other threads:[~2020-04-09 20:53 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-09 13:04 [GIT PULL 0/9] EFI fixes for v5.7-rc Ard Biesheuvel
2020-04-09 13:04 ` [PATCH 1/9] efi/cper: Use scnprintf() for avoiding potential buffer overflow Ard Biesheuvel
2020-04-09 13:04 ` [PATCH 2/9] efi/libstub/x86: remove redundant assignment to pointer hdr Ard Biesheuvel
2020-04-09 13:04 ` [PATCH 3/9] efi/x86: Move efi stub globals from .bss to .data Ard Biesheuvel
2020-04-09 20:05 ` Brian Gerst
2020-04-09 20:53 ` Brian Gerst [this message]
2020-04-09 21:08 ` Arvind Sankar
2020-04-10 8:20 ` Ard Biesheuvel
2020-04-10 15:16 ` Arvind Sankar
2020-04-10 16:03 ` Ard Biesheuvel
2020-04-10 18:01 ` Arvind Sankar
2020-04-10 18:03 ` Ard Biesheuvel
2020-04-10 19:03 ` Arvind Sankar
2020-04-11 1:03 ` Arvind Sankar
2020-04-09 13:04 ` [PATCH 4/9] efi/x86: Always relocate the kernel for EFI handover entry Ard Biesheuvel
2020-04-09 13:04 ` [PATCH 5/9] efi/arm: Deal with ADR going out of range in efi_enter_kernel() Ard Biesheuvel
2020-04-14 8:20 ` [tip: efi/urgent] " tip-bot2 for Ard Biesheuvel
2020-04-09 13:04 ` [PATCH 6/9] Documentation: efi/x86: clarify EFI handover protocol and its requirements Ard Biesheuvel
2020-04-14 8:20 ` [tip: efi/urgent] Documentation/x86, efi/x86: Clarify " tip-bot2 for Ard Biesheuvel
2020-04-09 13:04 ` [PATCH 7/9] efi/libstub/file: merge filename buffers to reduce stack usage Ard Biesheuvel
2020-04-14 8:20 ` [tip: efi/urgent] efi/libstub/file: Merge file name " tip-bot2 for Ard Biesheuvel
2020-04-09 13:04 ` [PATCH 8/9] efi/x86: Fix the deletion of variables in mixed mode Ard Biesheuvel
2020-04-09 13:04 ` [PATCH 9/9] efi/x86: Don't remap text<->rodata gap read-only for " Ard Biesheuvel
2020-04-14 8:20 ` [tip: efi/urgent] " tip-bot2 for Ard Biesheuvel
2020-04-09 19:01 ` [GIT PULL 0/9] EFI fixes for v5.7-rc Theodore Y. Ts'o
2020-04-09 19:04 ` Ard Biesheuvel
2020-04-09 20:16 ` Theodore Y. Ts'o
2020-04-09 21:29 ` Ard Biesheuvel
2020-04-09 23:57 ` Theodore Y. Ts'o
2020-04-10 7:08 ` Ard Biesheuvel
2020-04-10 13:54 ` Dave Young
2020-04-11 19:43 ` Theodore Y. Ts'o
2020-04-12 3:51 ` Dave Young
2020-04-13 14:07 ` David Howells
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