2023-07-11 09:38:04

by Petr Pavlu

Subject: [PATCH v2 1/2] x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG

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.

Fixes: dc5723b02e52 ("kbuild: add support for Clang LTO")
Signed-off-by: Petr Pavlu <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
---
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

2023-08-02 15:35:46

by tip-bot2 for Jacob Pan

Subject: [tip: x86/core] x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG

The following commit has been merged into the x86/core branch of tip:

Commit-ID: 973ab2d61f33dc85212c486e624af348c4eeb5c9
Gitweb: https://git.kernel.org/tip/973ab2d61f33dc85212c486e624af348c4eeb5c9
Author: Petr Pavlu <[email protected]>
AuthorDate: Tue, 11 Jul 2023 11:19:51 +02:00
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Wed, 02 Aug 2023 16:27:07 +02:00

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

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.

Fixes: dc5723b02e52 ("kbuild: add support for Clang LTO")
Signed-off-by: Petr Pavlu <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/kernel/vmlinux.lds.S | 2 +-
arch/x86/lib/retpoline.S | 4 ++--
tools/objtool/check.c | 2 +-
3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 03c885d..a4cd04c 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 3fd066d..3bea963 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:
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8936a05..e096eb3 100644
--- 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.", 12))
sec->noinstr = true;

/*

2023-08-03 23:52:15

by Josh Poimboeuf

Subject: Re: [tip: x86/core] x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG

On Wed, Aug 02, 2023 at 02:33:16PM -0000, tip-bot2 for Petr Pavlu wrote:
> The following commit has been merged into the x86/core branch of tip:
>
> Commit-ID: 973ab2d61f33dc85212c486e624af348c4eeb5c9
> Gitweb: https://git.kernel.org/tip/973ab2d61f33dc85212c486e624af348c4eeb5c9
> Author: Petr Pavlu <[email protected]>
> AuthorDate: Tue, 11 Jul 2023 11:19:51 +02:00
> Committer: Peter Zijlstra <[email protected]>
> CommitterDate: Wed, 02 Aug 2023 16:27:07 +02:00
>
> x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG
>

[...]

> --- 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.", 12))

Andy Cooper reported this should be 13.

--
Josh

2023-08-14 10:58:47

by tip-bot2 for Jacob Pan

Subject: [tip: x86/urgent] x86/retpoline,kprobes: Fix position of thunk sections with CONFIG_LTO_CLANG

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 79cd2a11224eab86d6673fe8a11d2046ae9d2757
Gitweb: https://git.kernel.org/tip/79cd2a11224eab86d6673fe8a11d2046ae9d2757
Author: Petr Pavlu <[email protected]>
AuthorDate: Tue, 11 Jul 2023 11:19:51 +02:00
Committer: Borislav Petkov (AMD) <[email protected]>
CommitterDate: Mon, 14 Aug 2023 11:44:19 +02:00

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/[email protected] ]

Fixes: dc5723b02e52 ("kbuild: add support for Clang LTO")
Signed-off-by: Petr Pavlu <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/kernel/vmlinux.lds.S | 8 ++++----
arch/x86/lib/retpoline.S | 8 ++++----
tools/objtool/check.c | 2 +-
3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index ef06211..dfb8783 100644
--- 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 132cedb..8db74d8 100644
--- 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 8936a05..e2ee10c 100644
--- 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;

/*