Commit 36d83c24 authored by H. Peter Anvin's avatar H. Peter Anvin Committed by Dave Hansen
Browse files

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



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: default avatarH. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Link: https://patch.msgid.link/20251216212606.1325678-11-hpa@zytor.com
parent f49ecf5e

arch/x86/entry/vdso/vdso32/system_call.S

+14 −4
Original line number Diff line number Diff line
@@ -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)

arch/x86/include/asm/vdso/sys_call.h

+3 −1
Original line number Diff line number Diff line
@@ -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"