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 53156389305f0598b6e85bdc0897ae7465c538e5..ab65626185fddecb65f23c76bb824aa6118d819e 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_alias_untrain_ret | (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 60e8b4c826b6d30c9e7c8481f656511475d5dd09..cd86aeb5fdd3eac07cf3f7872d3e22b771967f54 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_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
@@ -159,7 +159,7 @@ 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)
@@ -177,7 +177,7 @@ 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 30c81c0f17b23cf73655f3d640547e19e6909e6e..f7f34a0b101e1613e01b9943bb14f08e6209c95b 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -429,7 +429,7 @@ 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;
 
                /*