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

commit 79cd2a11224eab86d6673fe8a11d2046ae9d2757 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: 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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 6b137c0..78ccb5e 100644 (file)
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -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
@@ -154,8 +154,8 @@ 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

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 5a55ee2..65c5c44 100644 (file)
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -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
@@ -91,7 +91,7 @@ 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
@@ -102,7 +102,7 @@ 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)
@@ -120,7 +120,7 @@ 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

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8ec9776..7c4e61c 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -379,7 +379,7 @@ 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) {