diff mbox series

[1/2] x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG

Message ID 20230705081547.25130-2-petr.pavlu@suse.com
State New
Headers
Series x86/retpoline,kprobes: Fix the [__indirect_thunk_start, ..end] range |

Commit Message

Petr Pavlu July 5, 2023, 8:15 a.m. UTC 
  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 range [__indirect_thunk_start, __indirect_thunk_end] is
then empty.

A visible result is that function insn_is_indirect_jump() misbehaves and
optprobes become allowed in functions where they are not potentially
safe.

Fix the problem by using ".." as the first separator, for instance,
".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.

Fixes: dc5723b02e52 ("kbuild: add support for Clang LTO")
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
---
 arch/x86/kernel/vmlinux.lds.S | 2 +-
 arch/x86/lib/retpoline.S      | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

Comments

Peter Zijlstra July 5, 2023, 8:52 a.m. UTC | #1 
On Wed, Jul 05, 2023 at 10:15:46AM +0200, Petr Pavlu wrote:
> 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 range [__indirect_thunk_start, __indirect_thunk_end] is
> then empty.
> 
> A visible result is that function insn_is_indirect_jump() misbehaves and
> optprobes become allowed in functions where they are not potentially
> safe.
> 
> Fix the problem by using ".." as the first separator, for instance,
> ".text..__x86.indirect_thunk". This pattern is utilized by other

First I hear of this, but yes, indeed.

> 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.
> 
> Fixes: dc5723b02e52 ("kbuild: add support for Clang LTO")
> Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> ---
>  arch/x86/kernel/vmlinux.lds.S | 2 +-
>  arch/x86/lib/retpoline.S      | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 03c885d3640f..a4cd04c458df 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -134,7 +134,7 @@ SECTIONS
>  		SOFTIRQENTRY_TEXT
>  #ifdef CONFIG_RETPOLINE
>  		__indirect_thunk_start = .;
> -		*(.text.__x86.*)
> +		*(.text..__x86.*)
>  		__indirect_thunk_end = .;
>  #endif
>  		STATIC_CALL_TEXT
> diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
> index 3fd066d42ec0..3bea96341d00 100644
> --- a/arch/x86/lib/retpoline.S
> +++ b/arch/x86/lib/retpoline.S
> @@ -12,7 +12,7 @@
>  #include <asm/percpu.h>
>  #include <asm/frame.h>
>  
> -	.section .text.__x86.indirect_thunk
> +	.section .text..__x86.indirect_thunk
>  
>  
>  .macro POLINE reg
> @@ -131,7 +131,7 @@ SYM_CODE_END(__x86_indirect_jump_thunk_array)
>   */
>  #ifdef CONFIG_RETHUNK
>  
> -	.section .text.__x86.return_thunk
> +	.section .text..__x86.return_thunk
>  
>  /*
>   * Safety details here pertain to the AMD Zen{1,2} microarchitecture:
> -- 
> 2.35.3
>
diff mbox series

Patch

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 03c885d3640f..a4cd04c458df 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -134,7 +134,7 @@  SECTIONS
 		SOFTIRQENTRY_TEXT
 #ifdef CONFIG_RETPOLINE
 		__indirect_thunk_start = .;
-		*(.text.__x86.*)
+		*(.text..__x86.*)
 		__indirect_thunk_end = .;
 #endif
 		STATIC_CALL_TEXT
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 3fd066d42ec0..3bea96341d00 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -12,7 +12,7 @@ 
 #include <asm/percpu.h>
 #include <asm/frame.h>
 
-	.section .text.__x86.indirect_thunk
+	.section .text..__x86.indirect_thunk
 
 
 .macro POLINE reg
@@ -131,7 +131,7 @@  SYM_CODE_END(__x86_indirect_jump_thunk_array)
  */
 #ifdef CONFIG_RETHUNK
 
-	.section .text.__x86.return_thunk
+	.section .text..__x86.return_thunk
 
 /*
  * Safety details here pertain to the AMD Zen{1,2} microarchitecture: