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x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG

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The linker script arch/x86/kernel/vmlinux.lds.S matches the thunk
sections ".text.__x86.*" from arch/x86/lib/retpoline.S as follows:

  .text {
    [...]
    TEXT_TEXT
    [...]
    __indirect_thunk_start = .;
    *(.text.__x86.*)
    __indirect_thunk_end = .;
    [...]
  }

Macro TEXT_TEXT references TEXT_MAIN which normally expands to only
".text". However, with CONFIG_LTO_CLANG, TEXT_MAIN becomes
".text .text.[0-9a-zA-Z_]*" which wrongly matches also the thunk
sections. The output layout is then different than expected. For
instance, the currently defined range [__indirect_thunk_start,
__indirect_thunk_end] becomes empty.

Prevent the problem by using ".." as the first separator, for example,
".text..__x86.indirect_thunk". This pattern is utilized by other
explicit section names which start with one of the standard prefixes,
such as ".text" or ".data", and that need to be individually selected in
the linker script.

  [ nathan: Fix conflicts with SRSO and fold in fix issue brought up by
    Andrew Cooper in post-review:
    https://lore.kernel.org/20230803230323.1478869-1-andrew.cooper3@citrix.com ]

Fixes: dc5723b02e ("kbuild: add support for Clang LTO")
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230711091952.27944-2-petr.pavlu@suse.com
This commit is contained in:
Petr Pavlu 2023-07-11 11:19:51 +02:00 committed by Borislav Petkov (AMD)
parent e9fbc47b81
commit 79cd2a1122
3 changed files with 9 additions and 9 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

8
arch/x86/kernel/vmlinux.lds.S
View file

@ -134,15 +134,15 @@ SECTIONS
SOFTIRQENTRY_TEXT
#ifdef CONFIG_RETPOLINE
__indirect_thunk_start = .;
*(.text.__x86.indirect_thunk)
*(.text.__x86.return_thunk)
*(.text..__x86.indirect_thunk)
*(.text..__x86.return_thunk)
__indirect_thunk_end = .;
#endif
STATIC_CALL_TEXT
ALIGN_ENTRY_TEXT_BEGIN
#ifdef CONFIG_CPU_SRSO
*(.text.__x86.rethunk_untrain)
*(.text..__x86.rethunk_untrain)
#endif
ENTRY_TEXT
@ -153,7 +153,7 @@ SECTIONS
* definition.
*/
. = srso_untrain_ret_alias | (1 << 2) | (1 << 8) | (1 << 14) | (1 << 20);
*(.text.__x86.rethunk_safe)
*(.text..__x86.rethunk_safe)
#endif
ALIGN_ENTRY_TEXT_END
*(.gnu.warning)

8
arch/x86/lib/retpoline.S
View file

@ -13,7 +13,7 @@
#include <asm/frame.h>
#include <asm/nops.h>
.section .text.__x86.indirect_thunk
.section .text..__x86.indirect_thunk
.macro POLINE reg
@ -148,7 +148,7 @@ SYM_CODE_END(__x86_indirect_jump_thunk_array)
* As a result, srso_safe_ret_alias() becomes a safe return.
*/
#ifdef CONFIG_CPU_SRSO
.section .text.__x86.rethunk_untrain
.section .text..__x86.rethunk_untrain
SYM_START(srso_untrain_ret_alias, SYM_L_GLOBAL, SYM_A_NONE)
ANNOTATE_NOENDBR
@ -158,7 +158,7 @@ SYM_START(srso_untrain_ret_alias, SYM_L_GLOBAL, SYM_A_NONE)
SYM_FUNC_END(srso_untrain_ret_alias)
__EXPORT_THUNK(srso_untrain_ret_alias)
.section .text.__x86.rethunk_safe
.section .text..__x86.rethunk_safe
#endif
/* Needs a definition for the __x86_return_thunk alternative below. */
@ -172,7 +172,7 @@ SYM_START(srso_safe_ret_alias, SYM_L_GLOBAL, SYM_A_NONE)
int3
SYM_FUNC_END(srso_safe_ret_alias)
.section .text.__x86.return_thunk
.section .text..__x86.return_thunk
/*
* Safety details here pertain to the AMD Zen{1,2} microarchitecture:

2
tools/objtool/check.c
View file

@ -389,7 +389,7 @@ static int decode_instructions(struct objtool_file *file)
if (!strcmp(sec->name, ".noinstr.text") ||
!strcmp(sec->name, ".entry.text") ||
!strcmp(sec->name, ".cpuidle.text") ||
!strncmp(sec->name, ".text.__x86.", 12))
!strncmp(sec->name, ".text..__x86.", 13))
sec->noinstr = true;
/*