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

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commit 79cd2a1122 upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Petr Pavlu 2023-07-11 11:19:51 +02:00 • committed by Justin Hammond
parent 651b8c4c3f
commit dbeb65be5b
3 changed files with 9 additions and 9 deletions
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8
arch/x86/kernel/vmlinux.lds.S
View file

@ -134,7 +134,7 @@ SECTIONS
KPROBES_TEXT
ALIGN_ENTRY_TEXT_BEGIN
#ifdef CONFIG_CPU_SRSO
*(.text.__x86.rethunk_untrain)
*(.text..__x86.rethunk_untrain)
#endif
ENTRY_TEXT
@ -145,7 +145,7 @@ SECTIONS
* definition.
*/
. = srso_alias_untrain_ret | (1 << 2) | (1 << 8) | (1 << 14) | (1 << 20);
*(.text.__x86.rethunk_safe)
*(.text..__x86.rethunk_safe)
#endif
ALIGN_ENTRY_TEXT_END
SOFTIRQENTRY_TEXT
@ -155,8 +155,8 @@ SECTIONS
#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
} :text =0xcccc

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

@ -11,7 +11,7 @@
#include <asm/frame.h>
#include <asm/nops.h>
.section .text.__x86.indirect_thunk
.section .text..__x86.indirect_thunk
.macro RETPOLINE reg
ANNOTATE_INTRA_FUNCTION_CALL
@ -90,7 +90,7 @@ SYM_CODE_END(__x86_indirect_thunk_array)
* As a result, srso_alias_safe_ret() becomes a safe return.
*/
#ifdef CONFIG_CPU_SRSO
.section .text.__x86.rethunk_untrain
.section .text..__x86.rethunk_untrain
SYM_START(srso_alias_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)
UNWIND_HINT_FUNC
@ -100,7 +100,7 @@ SYM_START(srso_alias_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)
SYM_FUNC_END(srso_alias_untrain_ret)
__EXPORT_THUNK(srso_alias_untrain_ret)
.section .text.__x86.rethunk_safe
.section .text..__x86.rethunk_safe
#else
/* dummy definition for alternatives */
SYM_START(srso_alias_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)
@ -118,7 +118,7 @@ SYM_START(srso_alias_safe_ret, SYM_L_GLOBAL, SYM_A_NONE)
int3
SYM_FUNC_END(srso_alias_safe_ret)
.section .text.__x86.return_thunk
.section .text..__x86.return_thunk
SYM_CODE_START(srso_alias_return_thunk)
UNWIND_HINT_FUNC

2
tools/objtool/check.c
View file

@ -370,7 +370,7 @@ static int decode_instructions(struct objtool_file *file)
if (!strcmp(sec->name, ".noinstr.text") ||
!strcmp(sec->name, ".entry.text") ||
!strncmp(sec->name, ".text.__x86.", 12))
!strncmp(sec->name, ".text..__x86.", 13))
sec->noinstr = true;
for (offset = 0; offset < sec->sh.sh_size; offset += insn->len) {