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: 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

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index ef06211bae4ccd2991d8dc3a692633069273d0d2..dfb8783cb4c76646b10d9fed6900734dfda48f5a 100644 (file)
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -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)

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 132cedbf9e571e583ecf6684e143e9450298e712..8db74d811ce2e6376e74d4dee839b1c377573e8d 100644 (file)
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -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:

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8936a05f0e5acbb151e7547b01a23268d711dfcb..e2ee10ce7703f58fabfdab23eb72be3a8a062630 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -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;
 
                /*