diff mbox

[4/5] x86: jump_label: switch to jump_entry accessors

Message ID 20180628091135.GB2494@hirez.programming.kicks-ass.net (mailing list archive)
State New, archived
Headers show

Commit Message

Peter Zijlstra June 28, 2018, 9:11 a.m. UTC
On Wed, Jun 27, 2018 at 06:06:03PM +0200, Ard Biesheuvel wrote:
> In preparation of switching x86 to use place-relative references for
> the code, target and key members of struct jump_entry, replace direct
> references to the struct members with invocations of the new accessors.
> This will allow us to make the switch by modifying the accessors only.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

That just makes horrible code worse.. can't we do something like so
instead?

Comments

Ard Biesheuvel June 28, 2018, 9:14 a.m. UTC | #1
On 28 June 2018 at 11:11, Peter Zijlstra <peterz@infradead.org> wrote:
> On Wed, Jun 27, 2018 at 06:06:03PM +0200, Ard Biesheuvel wrote:
>> In preparation of switching x86 to use place-relative references for
>> the code, target and key members of struct jump_entry, replace direct
>> references to the struct members with invocations of the new accessors.
>> This will allow us to make the switch by modifying the accessors only.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>
> That just makes horrible code worse.. can't we do something like so
> instead?
>

Sure, I will incorporate that for v2.

>
> --- a/arch/x86/kernel/jump_label.c
> +++ b/arch/x86/kernel/jump_label.c
> @@ -42,52 +42,37 @@ static void __jump_label_transform(struc
>                                    void *(*poker)(void *, const void *, size_t),
>                                    int init)
>  {
> -       union jump_code_union code;
> +       union jump_code_union jmp = {
> +               { .jump = 0xe9,
> +                 .offset = jump_entry_target(entry) -
> +                           (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE), }
> +       };
>         const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
>         const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
> +       const unsigned char *expect, *code;
> +       int line;
>
>         if (type == JUMP_LABEL_JMP) {
>                 if (init) {
> -                       /*
> -                        * Jump label is enabled for the first time.
> -                        * So we expect a default_nop...
> -                        */
> -                       if (unlikely(memcmp((void *)entry->code, default_nop, 5)
> -                                    != 0))
> -                               bug_at((void *)entry->code, __LINE__);
> +                       expect = default_nop; line = __LINE__;
>                 } else {
> -                       /*
> -                        * ...otherwise expect an ideal_nop. Otherwise
> -                        * something went horribly wrong.
> -                        */
> -                       if (unlikely(memcmp((void *)entry->code, ideal_nop, 5)
> -                                    != 0))
> -                               bug_at((void *)entry->code, __LINE__);
> +                       expect = ideal_nop; line = __LINE__;
>                 }
>
> -               code.jump = 0xe9;
> -               code.offset = entry->target -
> -                               (entry->code + JUMP_LABEL_NOP_SIZE);
> +               code = &jmp.code;
>         } else {
> -               /*
> -                * We are disabling this jump label. If it is not what
> -                * we think it is, then something must have gone wrong.
> -                * If this is the first initialization call, then we
> -                * are converting the default nop to the ideal nop.
> -                */
>                 if (init) {
> -                       if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
> -                               bug_at((void *)entry->code, __LINE__);
> +                       expect = default_nop; line = __LINE__;
>                 } else {
> -                       code.jump = 0xe9;
> -                       code.offset = entry->target -
> -                               (entry->code + JUMP_LABEL_NOP_SIZE);
> -                       if (unlikely(memcmp((void *)entry->code, &code, 5) != 0))
> -                               bug_at((void *)entry->code, __LINE__);
> +                       expect = &jmp.code; line = __LINE__;
>                 }
> -               memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
> +
> +               code = ideal_nop;
>         }
>
> +       if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
> +               bug_at((void *)jump_entry_code(entry), line);
> +
>         /*
>          * Make text_poke_bp() a default fallback poker.
>          *
> @@ -96,11 +81,13 @@ static void __jump_label_transform(struc
>          * always nop being the 'currently valid' instruction
>          *
>          */
> -       if (poker)
> -               (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
> -       else
> -               text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE,
> -                            (void *)entry->code + JUMP_LABEL_NOP_SIZE);
> +       if (poker) {
> +               (*poker)((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE);
> +               return;
> +       }
> +
> +       text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE,
> +                    (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
>  }
>
>  void arch_jump_label_transform(struct jump_entry *entry,
diff mbox

Patch

--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -42,52 +42,37 @@  static void __jump_label_transform(struc
 				   void *(*poker)(void *, const void *, size_t),
 				   int init)
 {
-	union jump_code_union code;
+	union jump_code_union jmp = {
+		{ .jump = 0xe9,
+		  .offset = jump_entry_target(entry) -
+			    (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE), }
+	};
 	const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
 	const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
+	const unsigned char *expect, *code;
+	int line;
 
 	if (type == JUMP_LABEL_JMP) {
 		if (init) {
-			/*
-			 * Jump label is enabled for the first time.
-			 * So we expect a default_nop...
-			 */
-			if (unlikely(memcmp((void *)entry->code, default_nop, 5)
-				     != 0))
-				bug_at((void *)entry->code, __LINE__);
+			expect = default_nop; line = __LINE__;
 		} else {
-			/*
-			 * ...otherwise expect an ideal_nop. Otherwise
-			 * something went horribly wrong.
-			 */
-			if (unlikely(memcmp((void *)entry->code, ideal_nop, 5)
-				     != 0))
-				bug_at((void *)entry->code, __LINE__);
+			expect = ideal_nop; line = __LINE__;
 		}
 
-		code.jump = 0xe9;
-		code.offset = entry->target -
-				(entry->code + JUMP_LABEL_NOP_SIZE);
+		code = &jmp.code;
 	} else {
-		/*
-		 * We are disabling this jump label. If it is not what
-		 * we think it is, then something must have gone wrong.
-		 * If this is the first initialization call, then we
-		 * are converting the default nop to the ideal nop.
-		 */
 		if (init) {
-			if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
-				bug_at((void *)entry->code, __LINE__);
+			expect = default_nop; line = __LINE__;
 		} else {
-			code.jump = 0xe9;
-			code.offset = entry->target -
-				(entry->code + JUMP_LABEL_NOP_SIZE);
-			if (unlikely(memcmp((void *)entry->code, &code, 5) != 0))
-				bug_at((void *)entry->code, __LINE__);
+			expect = &jmp.code; line = __LINE__;
 		}
-		memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
+
+		code = ideal_nop;
 	}
 
+	if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
+		bug_at((void *)jump_entry_code(entry), line);
+
 	/*
 	 * Make text_poke_bp() a default fallback poker.
 	 *
@@ -96,11 +81,13 @@  static void __jump_label_transform(struc
 	 * always nop being the 'currently valid' instruction
 	 *
 	 */
-	if (poker)
-		(*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
-	else
-		text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE,
-			     (void *)entry->code + JUMP_LABEL_NOP_SIZE);
+	if (poker) {
+		(*poker)((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE);
+		return;
+	}
+
+	text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE,
+		     (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
 }
 
 void arch_jump_label_transform(struct jump_entry *entry,