linux-kernel - [PATCH 02/20] efi/libstub/x86: force 'hidden' visibility for extern declarations

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri,  3 Jan 2020 12:39:35 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Matthew Garrett <mjg59@...gle.com>
Subject: [PATCH 02/20] efi/libstub/x86: force 'hidden' visibility for extern declarations

Commit c3710de5065d ("efi/libstub/x86: Drop __efi_early() export and
efi_config struct") introduced a reference from C code in eboot.c to
the startup_32 symbol defined in the .S startup code. This results in
a GOT based reference to startup_32, and since GOT entries carry
absolute addresses, they need to be fixed up before they can be used.

On modern toolchains (binutils 2.26 or later), this reference is
relaxed into a R_386_GOTOFF relocation (or the analogous X86_64 one)
which never uses the absolute address in the entry, and so we get
away with not fixing up the GOT table before calling the EFI entry
point. However, GCC 4.6 combined with a binutils of the era (2.24)
will produce a true GOT indirected reference, resulting in a wrong
value to be returned for the address of startup_32() if the boot
code is not running at the address it was linked at.

Fortunately, we can easily override this behavior, and force GCC to
emit the GOTOFF relocations explicitly, by setting the visibility
pragma 'hidden'.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/boot/compressed/eboot.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index da04948d75ed..565ee4733579 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -6,6 +6,8 @@
  *
  * ----------------------------------------------------------------------- */

+#pragma GCC visibility push(hidden)
+
 #include <linux/efi.h>
 #include <linux/pci.h>

-- 
2.20.1