[PATCH v4 06/39] x86/asm: Fix VDSO DWARF generation with kernel IBT enabled

Josh Poimboeuf
2025-01-22T02:31:58Z

The DWARF .cfi_startproc annotation needs to be at the very beginning of
a function. But with kernel IBT that doesn't happen as ENDBR is
sneakily embedded in SYM_FUNC_START. As a result the DWARF unwinding
info is wrong at the beginning of all the VDSO functions.

Fix it by adding CFI_STARTPROC and CFI_ENDPROC to SYM_FUNC_START_* and
SYM_FUNC_END respectively. Note this only affects VDSO, as the CFI_*
macros are empty for the kernel proper.

Fixes: c4691712b546 ("x86/linkage: Add ENDBR to SYM_FUNC_START*()")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
arch/x86/entry/vdso/vdso-layout.lds.S | 2 +-
arch/x86/entry/vdso/vgetrandom-chacha.S | 2 --
arch/x86/entry/vdso/vsgx.S | 4 ----
arch/x86/include/asm/linkage.h | 29 +++++++++++++++++++------
arch/x86/include/asm/vdso.h | 1 -
5 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
index 872947c1004c..506c9800a5aa 100644
--- a/arch/x86/entry/vdso/vdso-layout.lds.S
+++ b/arch/x86/entry/vdso/vdso-layout.lds.S
@@ -1,5 +1,5 @@
/* SPDX-License-Identifier: GPL-2.0 */
-#include <asm/vdso.h>
+#include <asm/page_types.h>
#include <asm/vdso/vsyscall.h>

/*
diff --git a/arch/x86/entry/vdso/vgetrandom-chacha.S b/arch/x86/entry/vdso/vgetrandom-chacha.S
index cc82da9216fb..a33212594731 100644
--- a/arch/x86/entry/vdso/vgetrandom-chacha.S
+++ b/arch/x86/entry/vdso/vgetrandom-chacha.S
@@ -22,7 +22,6 @@ CONSTANTS: .octa 0x6b20657479622d323320646e61707865
* rcx: number of 64-byte blocks to write to output
*/
SYM_FUNC_START(__arch_chacha20_blocks_nostack)
- CFI_STARTPROC
.set output, %rdi
.set key, %rsi
.set counter, %rdx
@@ -175,5 +174,4 @@ SYM_FUNC_START(__arch_chacha20_blocks_nostack)
pxor temp,temp

ret
- CFI_ENDPROC
SYM_FUNC_END(__arch_chacha20_blocks_nostack)
diff --git a/arch/x86/entry/vdso/vsgx.S b/arch/x86/entry/vdso/vsgx.S
index 37a3d4c02366..c0342238c976 100644
--- a/arch/x86/entry/vdso/vsgx.S
+++ b/arch/x86/entry/vdso/vsgx.S
@@ -24,8 +24,6 @@
.section .text, "ax"

SYM_FUNC_START(__vdso_sgx_enter_enclave)
- /* Prolog */
- .cfi_startproc
push %rbp
.cfi_adjust_cfa_offset 8
.cfi_rel_offset %rbp, 0
@@ -143,8 +141,6 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
jle .Lout
jmp .Lenter_enclave

- .cfi_endproc
-
_ASM_VDSO_EXTABLE_HANDLE(.Lenclu_eenter_eresume, .Lhandle_exception)

SYM_FUNC_END(__vdso_sgx_enter_enclave)
diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index dc31b13b87a0..2866d57ef907 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -40,6 +40,10 @@

#ifdef __ASSEMBLY__

+#ifndef LINKER_SCRIPT
+#include <asm/dwarf2.h>
+#endif
+
#if defined(CONFIG_MITIGATION_RETHUNK) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO)
#define RET jmp __x86_return_thunk
#else /* CONFIG_MITIGATION_RETPOLINE */
@@ -112,40 +116,51 @@
# define SYM_FUNC_ALIAS_MEMFUNC SYM_FUNC_ALIAS
#endif

+#define __SYM_FUNC_START \
+ CFI_STARTPROC ASM_NL \
+ ENDBR
+
+#define __SYM_FUNC_END \
+ CFI_ENDPROC ASM_NL
+
/* SYM_TYPED_FUNC_START -- use for indirectly called globals, w/ CFI type */
#define SYM_TYPED_FUNC_START(name) \
SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_F_ALIGN) \
- ENDBR
+ __SYM_FUNC_START

/* SYM_FUNC_START -- use for global functions */
#define SYM_FUNC_START(name) \
SYM_START(name, SYM_L_GLOBAL, SYM_F_ALIGN) \
- ENDBR
+ __SYM_FUNC_START

/* SYM_FUNC_START_NOALIGN -- use for global functions, w/o alignment */
#define SYM_FUNC_START_NOALIGN(name) \
SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE) \
- ENDBR
+ __SYM_FUNC_START

/* SYM_FUNC_START_LOCAL -- use for local functions */
#define SYM_FUNC_START_LOCAL(name) \
SYM_START(name, SYM_L_LOCAL, SYM_F_ALIGN) \
- ENDBR
+ __SYM_FUNC_START

/* SYM_FUNC_START_LOCAL_NOALIGN -- use for local functions, w/o alignment */
#define SYM_FUNC_START_LOCAL_NOALIGN(name) \
SYM_START(name, SYM_L_LOCAL, SYM_A_NONE) \
- ENDBR
+ __SYM_FUNC_START

/* SYM_FUNC_START_WEAK -- use for weak functions */
#define SYM_FUNC_START_WEAK(name) \
SYM_START(name, SYM_L_WEAK, SYM_F_ALIGN) \
- ENDBR
+ __SYM_FUNC_START

/* SYM_FUNC_START_WEAK_NOALIGN -- use for weak functions, w/o alignment */
#define SYM_FUNC_START_WEAK_NOALIGN(name) \
SYM_START(name, SYM_L_WEAK, SYM_A_NONE) \
- ENDBR
+ __SYM_FUNC_START
+
+#define SYM_FUNC_END(name) \
+ __SYM_FUNC_END \
+ SYM_END(name, SYM_T_FUNC)

#endif /* _ASM_X86_LINKAGE_H */

diff --git a/arch/x86/include/asm/vdso.h b/arch/x86/include/asm/vdso.h
index d7f6592b74a9..0111c349bbc5 100644
--- a/arch/x86/include/asm/vdso.h
+++ b/arch/x86/include/asm/vdso.h
@@ -2,7 +2,6 @@
#ifndef _ASM_X86_VDSO_H
#define _ASM_X86_VDSO_H

-#include <asm/page_types.h>
#include <linux/linkage.h>
#include <linux/init.h>

--
2.48.1