Commit 860238af authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

x86_64/bug: Inline the UD1 



(Ab)use the static_call infrastructure to convert all:

  call __WARN_trap

instances into the desired:

  ud1 (%edx), %rdi

eliminating the CALL/RET, but more importantly, fixing the
fact that all WARNs will have:

  RIP: 0010:__WARN_trap+0

Basically, by making it a static_call trampoline call, objtool will
collect the callsites, and then the inline rewrite will hit the
special case and replace the code with the magic instruction.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251110115758.456717741@infradead.org
parent 11bb4944

arch/x86/include/asm/bug.h

+4 −1
Original line number Diff line number Diff line
@@ -140,6 +140,9 @@ do { \ 
#ifdef HAVE_ARCH_BUG_FORMAT_ARGS



#ifndef __ASSEMBLY__

#include <linux/static_call_types.h>

DECLARE_STATIC_CALL(WARN_trap, __WARN_trap);



struct pt_regs;

struct sysv_va_list { /* from AMD64 System V ABI */

	unsigned int gp_offset;
@@ -171,7 +174,7 @@ extern void *__warn_args(struct arch_va_list *args, struct pt_regs *regs); 
#define __WARN_print_arg(flags, format, arg...)				\

do {									\

	int __flags = (flags) | BUGFLAG_WARNING | BUGFLAG_ARGS ;	\

	__WARN_trap(__WARN_bug_entry(__flags, format), ## arg);		\

	static_call_mod(WARN_trap)(__WARN_bug_entry(__flags, format), ## arg); \

	asm (""); /* inhibit tail-call optimization */			\

} while (0)

arch/x86/kernel/static_call.c

+11 −2
Original line number Diff line number Diff line
@@ -26,6 +26,11 @@ static const u8 xor5rax[] = { 0x2e, 0x2e, 0x2e, 0x31, 0xc0 }; 


static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };



/*

 * ud1    (%edx),%rdi -- see __WARN_trap() / decode_bug()

 */

static const u8 warninsn[] = { 0x67, 0x48, 0x0f, 0xb9, 0x3a };



static u8 __is_Jcc(u8 *insn) /* Jcc.d32 */

{

	u8 ret = 0;
@@ -69,7 +74,10 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, 
			emulate = code;

			code = &xor5rax;

		}



		if (func == &__WARN_trap) {

			emulate = code;

			code = &warninsn;

		}

		break;



	case NOP:
@@ -128,7 +136,8 @@ static void __static_call_validate(u8 *insn, bool tail, bool tramp) 
	} else {

		if (opcode == CALL_INSN_OPCODE ||

		    !memcmp(insn, x86_nops[5], 5) ||

		    !memcmp(insn, xor5rax, 5))

		    !memcmp(insn, xor5rax, 5) ||

		    !memcmp(insn, warninsn, 5))

			return;

	}

arch/x86/kernel/traps.c

+4 −0
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ 
#include <linux/kexec.h>

#include <linux/sched.h>

#include <linux/sched/task_stack.h>

#include <linux/static_call.h>

#include <linux/timer.h>

#include <linux/init.h>

#include <linux/bug.h>
@@ -215,6 +216,9 @@ static inline unsigned long pt_regs_val(struct pt_regs *regs, int nr) 
}



#ifdef HAVE_ARCH_BUG_FORMAT_ARGS

DEFINE_STATIC_CALL(WARN_trap, __WARN_trap);

EXPORT_STATIC_CALL_TRAMP(WARN_trap);



/*

 * Create a va_list from an exception context.

 */