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

Message ID 20180627160604.8154-5-ard.biesheuvel@linaro.org
State New
Headers show
Series
  • add support for relative references in jump tables
Related show

Commit Message

Ard Biesheuvel June 27, 2018, 4:06 p.m.
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>

---
 arch/x86/kernel/jump_label.c | 43 ++++++++++++--------
 1 file changed, 26 insertions(+), 17 deletions(-)

-- 
2.11.0

Comments

Peter Zijlstra June 28, 2018, 9:11 a.m. | #1
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?


--- 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,
Ard Biesheuvel June 28, 2018, 9:14 a.m. | #2
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,

Patch

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index e56c95be2808..d64296092ef5 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -52,22 +52,24 @@  static void __jump_label_transform(struct jump_entry *entry,
 			 * 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__);
+			if (unlikely(memcmp((void *)jump_entry_code(entry),
+					    default_nop, 5) != 0))
+				bug_at((void *)jump_entry_code(entry),
+				       __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__);
+			if (unlikely(memcmp((void *)jump_entry_code(entry),
+					    ideal_nop, 5) != 0))
+				bug_at((void *)jump_entry_code(entry),
+				       __LINE__);
 		}
 
 		code.jump = 0xe9;
-		code.offset = entry->target -
-				(entry->code + JUMP_LABEL_NOP_SIZE);
+		code.offset = jump_entry_target(entry) -
+			      (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
 	} else {
 		/*
 		 * We are disabling this jump label. If it is not what
@@ -76,14 +78,18 @@  static void __jump_label_transform(struct jump_entry *entry,
 		 * 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__);
+			if (unlikely(memcmp((void *)jump_entry_code(entry),
+					    default_nop, 5) != 0))
+				bug_at((void *)jump_entry_code(entry),
+				       __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__);
+			code.offset = jump_entry_target(entry) -
+				(jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
+			if (unlikely(memcmp((void *)jump_entry_code(entry),
+				     &code, 5) != 0))
+				bug_at((void *)jump_entry_code(entry),
+				       __LINE__);
 		}
 		memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
 	}
@@ -97,10 +103,13 @@  static void __jump_label_transform(struct jump_entry *entry,
 	 *
 	 */
 	if (poker)
-		(*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
+		(*poker)((void *)jump_entry_code(entry), &code,
+			 JUMP_LABEL_NOP_SIZE);
 	else
-		text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE,
-			     (void *)entry->code + JUMP_LABEL_NOP_SIZE);
+		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,