linux-stable.git/arch/x86/boot, branch linux-5.4.y

x86/boot/compressed: prefer cc-option for CFLAGS additions

2025-06-27T10:02:50+00:00

commit 994f5f7816ff963f49269cfc97f63cb2e4edb84f upstream.

as-option tests new options using KBUILD_CFLAGS, which causes problems
when using as-option to update KBUILD_AFLAGS because many compiler
options are not valid assembler options.

This will be fixed in a follow up patch. Before doing so, move the
assembler test for -Wa,-mrelax-relocations=no from using as-option to
cc-option.

Link: https://lore.kernel.org/llvm/CAK7LNATcHt7GcXZ=jMszyH=+M_LC9Qr6yeAGRCBbE6xriLxtUQ@mail.gmail.com/
Suggested-by: Masahiro Yamada 
Reviewed-by: Nathan Chancellor 
Tested-by: Nathan Chancellor 
Signed-off-by: Nick Desaulniers 
Signed-off-by: Nathan Chancellor 
Tested-by: Linux Kernel Functional Testing 
Tested-by: Anders Roxell 
Signed-off-by: Masahiro Yamada 
Signed-off-by: Nathan Chancellor 
Signed-off-by: Greg Kroah-Hartman

x86/decompressor: Don't rely on upper 32 bits of GPRs being preserved

2023-09-23T08:59:41+00:00

[ Upstream commit 264b82fdb4989cf6a44a2bcd0c6ea05e8026b2ac ]

The 4-to-5 level mode switch trampoline disables long mode and paging in
order to be able to flick the LA57 bit. According to section 3.4.1.1 of
the x86 architecture manual [0], 64-bit GPRs might not retain the upper
32 bits of their contents across such a mode switch.

Given that RBP, RBX and RSI are live at this point, preserve them on the
stack, along with the return address that might be above 4G as well.

[0] Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1: Basic Architecture

  "Because the upper 32 bits of 64-bit general-purpose registers are
   undefined in 32-bit modes, the upper 32 bits of any general-purpose
   register are not preserved when switching from 64-bit mode to a 32-bit
   mode (to protected mode or compatibility mode). Software must not
   depend on these bits to maintain a value after a 64-bit to 32-bit
   mode switch."

Fixes: 194a9749c73d650c ("x86/boot/compressed/64: Handle 5-level paging boot if kernel is above 4G")
Signed-off-by: Ard Biesheuvel 
Signed-off-by: Borislav Petkov (AMD) 
Link: https://lore.kernel.org/r/20230807162720.545787-2-ardb@kernel.org
Signed-off-by: Sasha Levin

x86/boot: Annotate local functions

2023-09-23T08:59:41+00:00

[ Upstream commit deff8a24e1021fb39dddf5f6bc5832e0e3a632ea ]

.Lrelocated, .Lpaging_enabled, .Lno_longmode, and .Lin_pm32 are
self-standing local functions, annotate them as such and preserve "no
alignment".

The annotations do not generate anything yet.

Signed-off-by: Jiri Slaby 
Signed-off-by: Borislav Petkov 
Cc: Cao jin 
Cc: Greg Kroah-Hartman 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Kate Stewart 
Cc: "Kirill A. Shutemov" 
Cc: linux-arch@vger.kernel.org
Cc: Thomas Gleixner 
Cc: Wei Huang 
Cc: x86-ml 
Cc: Xiaoyao Li 
Link: https://lkml.kernel.org/r/20191011115108.12392-8-jslaby@suse.cz
Stable-dep-of: 264b82fdb498 ("x86/decompressor: Don't rely on upper 32 bits of GPRs being preserved")
Signed-off-by: Sasha Levin

x86/asm: Make more symbols local

2023-09-23T08:59:40+00:00

[ Upstream commit 30a2441cae7b149ff484a697bf9eb8de53240a4f ]

During the assembly cleanup patchset review, I found more symbols which
are used only locally. So make them really local by prepending ".L" to
them. Namely:

 - wakeup_idt is used only in realmode/rm/wakeup_asm.S.
 - in_pm32 is used only in boot/pmjump.S.
 - retint_user is used only in entry/entry_64.S, perhaps since commit
   2ec67971facc ("x86/entry/64/compat: Remove most of the fast system
   call machinery"), where entry_64_compat's caller was removed.

Drop GLOBAL from all of them too. I do not see more candidates in the
series.

Signed-off-by: Jiri Slaby 
Acked-by: Borislav Petkov 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: bp@alien8.de
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/20191011092213.31470-1-jslaby@suse.cz
Signed-off-by: Ingo Molnar 
Stable-dep-of: 264b82fdb498 ("x86/decompressor: Don't rely on upper 32 bits of GPRs being preserved")
Signed-off-by: Sasha Levin

x86/boot: Wrap literal addresses in absolute_pointer()

2023-06-09T08:29:01+00:00

commit aeb84412037b89e06f45e382f044da6f200e12f8 upstream.

GCC 11 (incorrectly[1]) assumes that literal values cast to (void *)
should be treated like a NULL pointer with an offset, and raises
diagnostics when doing bounds checking under -Warray-bounds. GCC 12
got "smarter" about finding these:

  In function 'rdfs8',
      inlined from 'vga_recalc_vertical' at /srv/code/arch/x86/boot/video-mode.c:124:29,
      inlined from 'set_mode' at /srv/code/arch/x86/boot/video-mode.c:163:3:
  /srv/code/arch/x86/boot/boot.h:114:9: warning: array subscript 0 is outside array bounds of 'u8[0]' {aka 'unsigned char[]'} [-Warray-bounds]
    114 |         asm volatile("movb %%fs:%1,%0" : "=q" (v) : "m" (*(u8 *)addr));
        |         ^~~

This has been solved in other places[2] already by using the recently
added absolute_pointer() macro. Do the same here.

  [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578
  [2] https://lore.kernel.org/all/20210912160149.2227137-1-linux@roeck-us.net/

Signed-off-by: Kees Cook 
Signed-off-by: Borislav Petkov 
Reviewed-by: Guenter Roeck 
Link: https://lore.kernel.org/r/20220227195918.705219-1-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman

x86/boot: Avoid using Intel mnemonics in AT&T syntax asm

2023-01-18T10:42:03+00:00

commit 7c6dd961d0c8e7e8f9fdc65071fb09ece702e18d upstream.

With 'GNU assembler (GNU Binutils for Debian) 2.39.90.20221231' the
build now reports:

  arch/x86/realmode/rm/../../boot/bioscall.S: Assembler messages:
  arch/x86/realmode/rm/../../boot/bioscall.S:35: Warning: found `movsd'; assuming `movsl' was meant
  arch/x86/realmode/rm/../../boot/bioscall.S:70: Warning: found `movsd'; assuming `movsl' was meant

  arch/x86/boot/bioscall.S: Assembler messages:
  arch/x86/boot/bioscall.S:35: Warning: found `movsd'; assuming `movsl' was meant
  arch/x86/boot/bioscall.S:70: Warning: found `movsd'; assuming `movsl' was meant

Which is due to:

  PR gas/29525

  Note that with the dropped CMPSD and MOVSD Intel Syntax string insn
  templates taking operands, mixed IsString/non-IsString template groups
  (with memory operands) cannot occur anymore. With that
  maybe_adjust_templates() becomes unnecessary (and is hence being
  removed).

More details: https://sourceware.org/bugzilla/show_bug.cgi?id=29525

Borislav Petkov further explains:

  " the particular problem here is is that the 'd' suffix is
    "conflicting" in the sense that you can have SSE mnemonics like movsD %xmm...
    and the same thing also for string ops (which is the case here) so apparently
    the agreement in binutils land is to use the always accepted suffixes 'l' or 'q'
    and phase out 'd' slowly... "

Fixes: 7a734e7dd93b ("x86, setup: "glove box" BIOS calls -- infrastructure")
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Acked-by: Borislav Petkov (AMD) 
Link: https://lore.kernel.org/r/Y71I3Ex2pvIxMpsP@hirez.programming.kicks-ass.net
Signed-off-by: Greg Kroah-Hartman

x86: link vdso and boot with -z noexecstack --no-warn-rwx-segments

2022-08-25T09:17:17+00:00

commit ffcf9c5700e49c0aee42dcba9a12ba21338e8136 upstream.

Users of GNU ld (BFD) from binutils 2.39+ will observe multiple
instances of a new warning when linking kernels in the form:

  ld: warning: arch/x86/boot/pmjump.o: missing .note.GNU-stack section implies executable stack
  ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
  ld: warning: arch/x86/boot/compressed/vmlinux has a LOAD segment with RWX permissions

Generally, we would like to avoid the stack being executable.  Because
there could be a need for the stack to be executable, assembler sources
have to opt-in to this security feature via explicit creation of the
.note.GNU-stack feature (which compilers create by default) or command
line flag --noexecstack.  Or we can simply tell the linker the
production of such sections is irrelevant and to link the stack as
--noexecstack.

LLVM's LLD linker defaults to -z noexecstack, so this flag isn't
strictly necessary when linking with LLD, only BFD, but it doesn't hurt
to be explicit here for all linkers IMO.  --no-warn-rwx-segments is
currently BFD specific and only available in the current latest release,
so it's wrapped in an ld-option check.

While the kernel makes extensive usage of ELF sections, it doesn't use
permissions from ELF segments.

Link: https://lore.kernel.org/linux-block/3af4127a-f453-4cf7-f133-a181cce06f73@kernel.dk/
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ba951afb99912da01a6e8434126b8fac7aa75107
Link: https://github.com/llvm/llvm-project/issues/57009
Reported-and-tested-by: Jens Axboe 
Suggested-by: Fangrui Song 
Signed-off-by: Nick Desaulniers 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

x86/boot: Add .text.* to setup.ld

2021-06-16T09:59:38+00:00

commit 2e7a858ba843d2e6ceab1ba996805411de51b340 upstream.

GCC puts the main function into .text.startup when compiled with -Os (or
-O2). This results in arch/x86/boot/main.c having a .text.startup
section which is currently not included explicitly in the linker script
setup.ld in the same directory.

The BFD linker places this orphan section immediately after .text, so
this still works. However, LLD git, since [1], is choosing to place it
immediately after the .bstext section instead (this is the first code
section). This plays havoc with the section layout that setup.elf
requires to create the setup header, for eg on 64-bit:

    LD      arch/x86/boot/setup.elf
  ld.lld: error: section .text.startup file range overlaps with .header
  >>> .text.startup range is [0x200040, 0x2001FE]
  >>> .header range is [0x2001EF, 0x20026B]

  ld.lld: error: section .header file range overlaps with .bsdata
  >>> .header range is [0x2001EF, 0x20026B]
  >>> .bsdata range is [0x2001FF, 0x200398]

  ld.lld: error: section .bsdata file range overlaps with .entrytext
  >>> .bsdata range is [0x2001FF, 0x200398]
  >>> .entrytext range is [0x20026C, 0x2002D3]

  ld.lld: error: section .text.startup virtual address range overlaps
  with .header
  >>> .text.startup range is [0x40, 0x1FE]
  >>> .header range is [0x1EF, 0x26B]

  ld.lld: error: section .header virtual address range overlaps with
  .bsdata
  >>> .header range is [0x1EF, 0x26B]
  >>> .bsdata range is [0x1FF, 0x398]

  ld.lld: error: section .bsdata virtual address range overlaps with
  .entrytext
  >>> .bsdata range is [0x1FF, 0x398]
  >>> .entrytext range is [0x26C, 0x2D3]

  ld.lld: error: section .text.startup load address range overlaps with
  .header
  >>> .text.startup range is [0x40, 0x1FE]
  >>> .header range is [0x1EF, 0x26B]

  ld.lld: error: section .header load address range overlaps with
  .bsdata
  >>> .header range is [0x1EF, 0x26B]
  >>> .bsdata range is [0x1FF, 0x398]

  ld.lld: error: section .bsdata load address range overlaps with
  .entrytext
  >>> .bsdata range is [0x1FF, 0x398]
  >>> .entrytext range is [0x26C, 0x2D3]

Add .text.* to the .text output section to fix this, and also prevent
any future surprises if the compiler decides to create other such
sections.

[1] https://reviews.llvm.org/D75225

Signed-off-by: Arvind Sankar 
Signed-off-by: Kees Cook 
Signed-off-by: Ingo Molnar 
Tested-by: Nick Desaulniers 
Tested-by: Sedat Dilek 
Reviewed-by: Kees Cook 
Reviewed-by: Ard Biesheuvel 
Reviewed-by: Fangrui Song 
Link: https://lore.kernel.org/r/20200731230820.1742553-5-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman

x86/asm: Replace __force_order with a memory clobber

2020-10-29T08:58:01+00:00

[ Upstream commit aa5cacdc29d76a005cbbee018a47faa6e724dd2d ]

The CRn accessor functions use __force_order as a dummy operand to
prevent the compiler from reordering CRn reads/writes with respect to
each other.

The fact that the asm is volatile should be enough to prevent this:
volatile asm statements should be executed in program order. However GCC
4.9.x and 5.x have a bug that might result in reordering. This was fixed
in 8.1, 7.3 and 6.5. Versions prior to these, including 5.x and 4.9.x,
may reorder volatile asm statements with respect to each other.

There are some issues with __force_order as implemented:
- It is used only as an input operand for the write functions, and hence
  doesn't do anything additional to prevent reordering writes.
- It allows memory accesses to be cached/reordered across write
  functions, but CRn writes affect the semantics of memory accesses, so
  this could be dangerous.
- __force_order is not actually defined in the kernel proper, but the
  LLVM toolchain can in some cases require a definition: LLVM (as well
  as GCC 4.9) requires it for PIE code, which is why the compressed
  kernel has a definition, but also the clang integrated assembler may
  consider the address of __force_order to be significant, resulting in
  a reference that requires a definition.

Fix this by:
- Using a memory clobber for the write functions to additionally prevent
  caching/reordering memory accesses across CRn writes.
- Using a dummy input operand with an arbitrary constant address for the
  read functions, instead of a global variable. This will prevent reads
  from being reordered across writes, while allowing memory loads to be
  cached/reordered across CRn reads, which should be safe.

Signed-off-by: Arvind Sankar 
Signed-off-by: Borislav Petkov 
Reviewed-by: Kees Cook 
Reviewed-by: Miguel Ojeda 
Tested-by: Nathan Chancellor 
Tested-by: Sedat Dilek 
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82602
Link: https://lore.kernel.org/lkml/20200527135329.1172644-1-arnd@arndb.de/
Link: https://lkml.kernel.org/r/20200902232152.3709896-1-nivedita@alum.mit.edu
Signed-off-by: Sasha Levin

x86/boot/compressed: Disable relocation relaxation

2020-09-23T10:40:46+00:00

commit 09e43968db40c33a73e9ddbfd937f46d5c334924 upstream.

The x86-64 psABI [0] specifies special relocation types
(R_X86_64_[REX_]GOTPCRELX) for indirection through the Global Offset
Table, semantically equivalent to R_X86_64_GOTPCREL, which the linker
can take advantage of for optimization (relaxation) at link time. This
is supported by LLD and binutils versions 2.26 onwards.

The compressed kernel is position-independent code, however, when using
LLD or binutils versions before 2.27, it must be linked without the -pie
option. In this case, the linker may optimize certain instructions into
a non-position-independent form, by converting foo@GOTPCREL(%rip) to $foo.

This potential issue has been present with LLD and binutils-2.26 for a
long time, but it has never manifested itself before now:

- LLD and binutils-2.26 only relax
	movq	foo@GOTPCREL(%rip), %reg
  to
	leaq	foo(%rip), %reg
  which is still position-independent, rather than
	mov	$foo, %reg
  which is permitted by the psABI when -pie is not enabled.

- GCC happens to only generate GOTPCREL relocations on mov instructions.

- CLang does generate GOTPCREL relocations on non-mov instructions, but
  when building the compressed kernel, it uses its integrated assembler
  (due to the redefinition of KBUILD_CFLAGS dropping -no-integrated-as),
  which has so far defaulted to not generating the GOTPCRELX
  relocations.

Nick Desaulniers reports [1,2]:

  "A recent change [3] to a default value of configuration variable
   (ENABLE_X86_RELAX_RELOCATIONS OFF -> ON) in LLVM now causes Clang's
   integrated assembler to emit R_X86_64_GOTPCRELX/R_X86_64_REX_GOTPCRELX
   relocations. LLD will relax instructions with these relocations based
   on whether the image is being linked as position independent or not.
   When not, then LLD will relax these instructions to use absolute
   addressing mode (R_RELAX_GOT_PC_NOPIC). This causes kernels built with
   Clang and linked with LLD to fail to boot."

Patch series [4] is a solution to allow the compressed kernel to be
linked with -pie unconditionally, but even if merged is unlikely to be
backported. As a simple solution that can be applied to stable as well,
prevent the assembler from generating the relaxed relocation types using
the -mrelax-relocations=no option. For ease of backporting, do this
unconditionally.

[0] https://gitlab.com/x86-psABIs/x86-64-ABI/-/blob/master/x86-64-ABI/linker-optimization.tex#L65
[1] https://lore.kernel.org/lkml/20200807194100.3570838-1-ndesaulniers@google.com/
[2] https://github.com/ClangBuiltLinux/linux/issues/1121
[3] https://reviews.llvm.org/rGc41a18cf61790fc898dcda1055c3efbf442c14c0
[4] https://lore.kernel.org/lkml/20200731202738.2577854-1-nivedita@alum.mit.edu/

Reported-by: Nick Desaulniers 
Signed-off-by: Arvind Sankar 
Signed-off-by: Ingo Molnar 
Tested-by: Nick Desaulniers 
Tested-by: Sedat Dilek 
Acked-by: Ard Biesheuvel 
Reviewed-by: Nick Desaulniers 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200812004308.1448603-1-nivedita@alum.mit.edu
Signed-off-by: Greg Kroah-Hartman