Commit 79cd2a11 authored by Petr Pavlu's avatar Petr Pavlu Committed by Borislav Petkov (AMD)
Browse files

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

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: dc5723b0 ("kbuild: add support for Clang LTO")
Signed-off-by: default avatarPetr Pavlu <petr.pavlu@suse.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarNathan Chancellor <nathan@kernel.org>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230711091952.27944-2-petr.pavlu@suse.com
parent e9fbc47b

arch/x86/kernel/vmlinux.lds.S

+4 −4
Original line number Diff line number Diff line
@@ -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)

arch/x86/lib/retpoline.S

+4 −4
Original line number Diff line number Diff line
@@ -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:

tools/objtool/check.c

+1 −1
Original line number Diff line number Diff line
@@ -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;



		/*