From: Petr Pavlu <petr.pavlu@suse.com>
Date: Tue, 11 Jul 2023 11:19:51 +0200
Subject: x86/retpoline,kprobes: Fix position of thunk sections with
 CONFIG_LTO_CLANG
Git-commit: 79cd2a11224eab86d6673fe8a11d2046ae9d2757
Patch-mainline: v6.5-rc7
References: git-fixes

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: dc5723b02e52 ("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

Acked-by: nborisov <nik.borisov@suse.com>
---
 arch/x86/kernel/vmlinux.lds.S |    8 ++++----
 arch/x86/lib/retpoline.S      |    8 ++++----
 2 files changed, 8 insertions(+), 8 deletions(-)

--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -122,13 +122,13 @@ 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
 		ALIGN_ENTRY_TEXT_BEGIN
 #ifdef CONFIG_CPU_SRSO
-		*(.text.__x86.rethunk_untrain)
+		*(.text..__x86.rethunk_untrain)
 #endif
 		ENTRY_TEXT
 		IRQENTRY_TEXT
@@ -138,7 +138,7 @@ 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)
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -10,7 +10,7 @@
 #include <asm/nops.h>
 
 .macro THUNK reg
-	.section .text.__x86.indirect_thunk
+	.section .text..__x86.indirect_thunk
 
 ENTRY(__x86_indirect_thunk_\reg)
 	CFI_STARTPROC
@@ -63,7 +63,7 @@ GENERATE_THUNK(r15)
  * 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
 
 .globl srso_untrain_ret_alias;
 srso_untrain_ret_alias:
@@ -73,7 +73,7 @@ srso_untrain_ret_alias:
 ENDPROC(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. */
@@ -93,7 +93,7 @@ ENDPROC(srso_safe_ret_alias)
  * for the compiler to generate JMPs to it.
  */
 
-	.section .text.__x86.return_thunk
+	.section .text..__x86.return_thunk
 
 /*
  * Safety details here pertain to the AMD Zen{1,2} microarchitecture: