linux-stable.git/arch/x86/kernel/vmlinux.lds.S, branch linux-4.4.y

x86_64: Fix jiffies ODR violation

2020-06-20T08:23:15+00:00

commit d8ad6d39c35d2b44b3d48b787df7f3359381dcbf upstream.

'jiffies' and 'jiffies_64' are meant to alias (two different symbols that
share the same address).  Most architectures make the symbols alias to the
same address via a linker script assignment in their
arch//kernel/vmlinux.lds.S:

jiffies = jiffies_64;

which is effectively a definition of jiffies.

jiffies and jiffies_64 are both forward declared for all architectures in
include/linux/jiffies.h. jiffies_64 is defined in kernel/time/timer.c.

x86_64 was peculiar in that it wasn't doing the above linker script
assignment, but rather was:
1. defining jiffies in arch/x86/kernel/time.c instead via the linker script.
2. overriding the symbol jiffies_64 from kernel/time/timer.c in
arch/x86/kernel/vmlinux.lds.s via 'jiffies_64 = jiffies;'.

As Fangrui notes:

  In LLD, symbol assignments in linker scripts override definitions in
  object files. GNU ld appears to have the same behavior. It would
  probably make sense for LLD to error "duplicate symbol" but GNU ld
  is unlikely to adopt for compatibility reasons.

This results in an ODR violation (UB), which seems to have survived
thus far. Where it becomes harmful is when;

1. -fno-semantic-interposition is used:

As Fangrui notes:

  Clang after LLVM commit 5b22bcc2b70d
  ("[X86][ELF] Prefer to lower MC_GlobalAddress operands to .Lfoo$local")
  defaults to -fno-semantic-interposition similar semantics which help
  -fpic/-fPIC code avoid GOT/PLT when the referenced symbol is defined
  within the same translation unit. Unlike GCC
  -fno-semantic-interposition, Clang emits such relocations referencing
  local symbols for non-pic code as well.

This causes references to jiffies to refer to '.Ljiffies$local' when
jiffies is defined in the same translation unit. Likewise, references to
jiffies_64 become references to '.Ljiffies_64$local' in translation units
that define jiffies_64.  Because these differ from the names used in the
linker script, they will not be rewritten to alias one another.

2. Full LTO

Full LTO effectively treats all source files as one translation
unit, causing these local references to be produced everywhere.  When
the linker processes the linker script, there are no longer any
references to jiffies_64' anywhere to replace with 'jiffies'.  And
thus '.Ljiffies$local' and '.Ljiffies_64$local' no longer alias
at all.

In the process of porting patches enabling Full LTO from arm64 to x86_64,
spooky bugs have been observed where the kernel appeared to boot, but init
doesn't get scheduled.

Avoid the ODR violation by matching other architectures and define jiffies
only by linker script.  For -fno-semantic-interposition + Full LTO, there
is no longer a global definition of jiffies for the compiler to produce a
local symbol which the linker script won't ensure aliases to jiffies_64.

Fixes: 40747ffa5aa8 ("asmlinkage: Make jiffies visible")
Reported-by: Nathan Chancellor 
Reported-by: Alistair Delva 
Debugged-by: Nick Desaulniers 
Debugged-by: Sami Tolvanen 
Suggested-by: Fangrui Song 
Signed-off-by: Bob Haarman 
Signed-off-by: Thomas Gleixner 
Tested-by: Sedat Dilek  # build+boot on
Reviewed-by: Andi Kleen 
Reviewed-by: Josh Poimboeuf 
Cc: stable@vger.kernel.org
Link: https://github.com/ClangBuiltLinux/linux/issues/852
Link: https://lkml.kernel.org/r/20200602193100.229287-1-inglorion@google.com
Signed-off-by: Greg Kroah-Hartman

Revert "x86/build: Move _etext to actual end of .text"

2019-06-11T10:24:12+00:00

This reverts commit 392bef709659abea614abfe53cf228e7a59876a4.

It seems to cause lots of problems when using the gold linker, and no
one really needs this at the moment, so just revert it from the stable
trees.

Cc: Sami Tolvanen 
Reported-by: Kees Cook 
Cc: Borislav Petkov 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Reported-by: Alec Ari 
Cc: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

x86/build: Move _etext to actual end of .text

2019-06-11T10:23:56+00:00

[ Upstream commit 392bef709659abea614abfe53cf228e7a59876a4 ]

When building x86 with Clang LTO and CFI, CFI jump regions are
automatically added to the end of the .text section late in linking. As a
result, the _etext position was being labelled before the appended jump
regions, causing confusion about where the boundaries of the executable
region actually are in the running kernel, and broke at least the fault
injection code. This moves the _etext mark to outside (and immediately
after) the .text area, as it already the case on other architectures
(e.g. arm64, arm).

Reported-and-tested-by: Sami Tolvanen 
Signed-off-by: Kees Cook 
Cc: Borislav Petkov 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/20190423183827.GA4012@beast
Signed-off-by: Ingo Molnar 
Signed-off-by: Sasha Levin

x86/build: Mark per-CPU symbols as absolute explicitly for LLD

2019-04-27T07:33:53+00:00

[ Upstream commit d071ae09a4a1414c1433d5ae9908959a7325b0ad ]

Accessing per-CPU variables is done by finding the offset of the
variable in the per-CPU block and adding it to the address of the
respective CPU's block.

Section 3.10.8 of ld.bfd's documentation states:

  For expressions involving numbers, relative addresses and absolute
  addresses, ld follows these rules to evaluate terms:

  Other binary operations, that is, between two relative addresses
  not in the same section, or between a relative address and an
  absolute address, first convert any non-absolute term to an
  absolute address before applying the operator."

Note that LLVM's linker does not adhere to the GNU ld's implementation
and as such requires implicitly-absolute terms to be explicitly marked
as absolute in the linker script. If not, it fails currently with:

  ld.lld: error: ./arch/x86/kernel/vmlinux.lds:153: at least one side of the expression must be absolute
  ld.lld: error: ./arch/x86/kernel/vmlinux.lds:154: at least one side of the expression must be absolute
  Makefile:1040: recipe for target 'vmlinux' failed

This is not a functional change for ld.bfd which converts the term to an
absolute symbol anyways as specified above.

Based on a previous submission by Tri Vo .

Reported-by: Dmitry Golovin 
Signed-off-by: Rafael Ávila de Espíndola 
[ Update commit message per Boris' and Michael's suggestions. ]
Signed-off-by: Nick Desaulniers 
[ Massage commit message more, fix typos. ]
Signed-off-by: Borislav Petkov 
Tested-by: Dmitry Golovin 
Cc: "H. Peter Anvin" 
Cc: Andy Lutomirski 
Cc: Brijesh Singh 
Cc: Cao Jin 
Cc: Ingo Molnar 
Cc: Joerg Roedel 
Cc: Masahiro Yamada 
Cc: Masami Hiramatsu 
Cc: Thomas Gleixner 
Cc: Tri Vo 
Cc: dima@golovin.in
Cc: morbo@google.com
Cc: x86-ml 
Link: https://lkml.kernel.org/r/20181219190145.252035-1-ndesaulniers@google.com
Signed-off-by: Sasha Levin

x86/alternatives: Add an auxilary section

2018-07-17T09:31:44+00:00

commit 337e4cc84021212a87b04b77b65cccc49304909e upstream

Add .altinstr_aux for additional instructions which will be used
before and/or during patching. All stuff which needs more
sophisticated patching should go there. See next patch.

Signed-off-by: Borislav Petkov 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1453842730-28463-8-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar 
Signed-off-by: Srivatsa S. Bhat 
Reviewed-by: Matt Helsley (VMware) 
Reviewed-by: Alexey Makhalov 
Reviewed-by: Bo Gan 
Signed-off-by: Greg Kroah-Hartman

retpoline: Introduce start/end markers of indirect thunk

2018-01-23T18:50:17+00:00

commit 736e80a4213e9bbce40a7c050337047128b472ac upstream.

Introduce start/end markers of __x86_indirect_thunk_* functions.
To make it easy, consolidate .text.__x86.indirect_thunk.* sections
to one .text.__x86.indirect_thunk section and put it in the
end of kernel text section and adds __indirect_thunk_start/end
so that other subsystem (e.g. kprobes) can identify it.

Signed-off-by: Masami Hiramatsu 
Signed-off-by: Thomas Gleixner 
Acked-by: David Woodhouse 
Cc: Andi Kleen 
Cc: Peter Zijlstra 
Cc: Ananth N Mavinakayanahalli 
Cc: Arjan van de Ven 
Cc: Greg Kroah-Hartman 
Link: https://lkml.kernel.org/r/151629206178.10241.6828804696410044771.stgit@devbox
Signed-off-by: Greg Kroah-Hartman

kexec: split kexec_load syscall from kexec core code

2015-09-10T20:29:01+00:00

There are two kexec load syscalls, kexec_load another and kexec_file_load.
 kexec_file_load has been splited as kernel/kexec_file.c.  In this patch I
split kexec_load syscall code to kernel/kexec.c.

And add a new kconfig option KEXEC_CORE, so we can disable kexec_load and
use kexec_file_load only, or vice verse.

The original requirement is from Ted Ts'o, he want kexec kernel signature
being checked with CONFIG_KEXEC_VERIFY_SIG enabled.  But kexec-tools use
kexec_load syscall can bypass the checking.

Vivek Goyal proposed to create a common kconfig option so user can compile
in only one syscall for loading kexec kernel.  KEXEC/KEXEC_FILE selects
KEXEC_CORE so that old config files still work.

Because there's general code need CONFIG_KEXEC_CORE, so I updated all the
architecture Kconfig with a new option KEXEC_CORE, and let KEXEC selects
KEXEC_CORE in arch Kconfig.  Also updated general kernel code with to
kexec_load syscall.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Dave Young 
Cc: Eric W. Biederman 
Cc: Vivek Goyal 
Cc: Petr Tesarik 
Cc: Theodore Ts'o 
Cc: Josh Boyer 
Cc: David Howells 
Cc: Geert Uytterhoeven 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

x86-64: Use RIP-relative addressing for most per-CPU accesses

2014-11-04T19:43:14+00:00

Observing that per-CPU data (in the SMP case) is reachable by
exploiting 64-bit address wraparound (building on the default kernel
load address being at 16Mb), the one byte shorter RIP-relative
addressing form can be used for most per-CPU accesses. The one
exception are the "stable" reads, where the use of the "P" operand
modifier prevents the compiler from using RIP-relative addressing, but
is unavoidable due to the use of the "p" constraint (side note: with
gcc 4.9.x the intended effect of this isn't being achieved anymore,
see gcc bug 63637).

With the dependency on the minimum kernel load address, arbitrarily
low values for CONFIG_PHYSICAL_START are now no longer possible. A
link time assertion is being added, directing to the need to increase
that value when it triggers.

Signed-off-by: Jan Beulich 
Link: http://lkml.kernel.org/r/5458A1780200007800044A9D@mail.emea.novell.com
Signed-off-by: Thomas Gleixner

x86, vdso: Zero-pad the VVAR page

2014-03-18T19:52:44+00:00

By coincidence, the VVAR page is at the end of an ELF segment.  As a
result, if it ends up being a partial page, the kernel loader will
leave garbage behind at the end of the vvar page.  Zero-pad it to a
full page to fix this issue.

This has probably been broken since the VVAR page was introduced.
On QEMU, if you dump the run-time contents of the VVAR page, you can
find entertaining strings from seabios left behind.

It's remotely possible that this is a security bug -- conceivably
there's some BIOS out there that leaves something sensitive in the
few K of memory that is exposed to userspace.

Signed-off-by: Stefani Seibold 
Link: http://lkml.kernel.org/r/1395094933-14252-12-git-send-email-stefani@seibold.net
Signed-off-by: H. Peter Anvin

x86, vdso: Make vsyscall_gtod_data handling x86 generic

2014-03-18T19:51:52+00:00

This patch move the vsyscall_gtod_data handling out of vsyscall_64.c
into an additonal file vsyscall_gtod.c to make the functionality
available for x86 32 bit kernel.

It also adds a new vsyscall_32.c which setup the VVAR page.

Reviewed-by: Andy Lutomirski 
Signed-off-by: Stefani Seibold 
Link: http://lkml.kernel.org/r/1395094933-14252-2-git-send-email-stefani@seibold.net
Signed-off-by: H. Peter Anvin