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x86/entry/vdso32: When using int $0x80, use it directly

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When neither sysenter32 nor syscall32 is available (on either
FRED-capable 64-bit hardware or old 32-bit hardware), there is no
reason to do a bunch of stack shuffling in __kernel_vsyscall.
Unfortunately, just overwriting the initial "push" instructions will
mess up the CFI annotations, so suffer the 3-byte NOP if not
applicable.

Similarly, inline the int $0x80 when doing inline system calls in the
vdso instead of calling __kernel_vsyscall.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://patch.msgid.link/20251216212606.1325678-11-hpa@zytor.com
This commit is contained in:
H. Peter Anvin
2025-12-16 13:26:04 -08:00
committed by Dave Hansen
parent f49ecf5e11
commit 36d83c249e
2 changed files with 17 additions and 5 deletions
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18
arch/x86/entry/vdso/vdso32/system_call.S
View File

@@ -14,6 +14,18 @@
ALIGN
__kernel_vsyscall:
CFI_STARTPROC
/*
* If using int $0x80, there is no reason to muck about with the
* stack here. Unfortunately just overwriting the push instructions
* would mess up the CFI annotations, but it is only a 3-byte
* NOP in that case. This could be avoided by patching the
* vdso symbol table (not the code) and entry point, but that
* would a fair bit of tooling work or by simply compiling
* two different vDSO images, but that doesn't seem worth it.
*/
ALTERNATIVE "int $0x80; ret", "", X86_FEATURE_SYSFAST32
/*
* Reshuffle regs so that all of any of the entry instructions
* will preserve enough state.
@@ -52,11 +64,9 @@ __kernel_vsyscall:
#define SYSENTER_SEQUENCE "movl %esp, %ebp; sysenter"
#define SYSCALL_SEQUENCE "movl %ecx, %ebp; syscall"
/* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */
ALTERNATIVE_2 "", SYSENTER_SEQUENCE, X86_FEATURE_SYSFAST32, \
SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32
ALTERNATIVE SYSENTER_SEQUENCE, SYSCALL_SEQUENCE, X86_FEATURE_SYSCALL32
/* Enter using int $0x80 */
/* Re-enter using int $0x80 */
int $0x80
SYM_INNER_LABEL(int80_landing_pad, SYM_L_GLOBAL)

4
arch/x86/include/asm/vdso/sys_call.h
View File

@@ -20,7 +20,9 @@
# define __sys_reg4 "r10"
# define __sys_reg5 "r8"
#else
# define __sys_instr "call __kernel_vsyscall"
# define __sys_instr ALTERNATIVE("ds;ds;ds;int $0x80", \
"call __kernel_vsyscall", \
X86_FEATURE_SYSFAST32)
# define __sys_clobber "memory"
# define __sys_nr(x,y) __NR_ ## x ## y
# define __sys_reg1 "ebx"