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Subject[tip: x86/core] x86/alternative: Simplify int3_selftest_ip
The following commit has been merged into the x86/core branch of tip:

Commit-ID: 99c95c5d4f1027130d555fdb27b576520894827d
Gitweb: https://git.kernel.org/tip/99c95c5d4f1027130d555fdb27b576520894827d
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 08 Mar 2022 16:30:37 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 15 Mar 2022 10:32:40 +01:00

x86/alternative: Simplify int3_selftest_ip

Similar to ibt_selftest_ip, apply the same pattern.

Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.700456643@infradead.org
---
arch/x86/kernel/alternative.c | 21 +++++++--------------
1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index b4470ea..14d1003 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -719,7 +719,7 @@ asm (
" .popsection\n"
);

-extern __initdata unsigned long int3_selftest_ip; /* defined in asm below */
+extern void int3_selftest_ip(void); /* defined in asm below */

static int __init
int3_exception_notify(struct notifier_block *self, unsigned long val, void *data)
@@ -733,14 +733,15 @@ int3_exception_notify(struct notifier_block *self, unsigned long val, void *data
if (val != DIE_INT3)
return NOTIFY_DONE;

- if (regs->ip - INT3_INSN_SIZE != int3_selftest_ip)
+ if (regs->ip - INT3_INSN_SIZE != (unsigned long)&int3_selftest_ip)
return NOTIFY_DONE;

int3_emulate_call(regs, (unsigned long)&int3_magic);
return NOTIFY_STOP;
}

-static void __init int3_selftest(void)
+/* Must be noinline to ensure uniqueness of int3_selftest_ip. */
+static noinline void __init int3_selftest(void)
{
static __initdata struct notifier_block int3_exception_nb = {
.notifier_call = int3_exception_notify,
@@ -753,18 +754,10 @@ static void __init int3_selftest(void)
/*
* Basically: int3_magic(&val); but really complicated :-)
*
- * Stick the address of the INT3 instruction into int3_selftest_ip,
- * then trigger the INT3, padded with NOPs to match a CALL instruction
- * length.
+ * INT3 padded with NOP to CALL_INSN_SIZE. The int3_exception_nb
+ * notifier above will emulate CALL for us.
*/
- asm volatile ("1: int3; nop; nop; nop; nop\n\t"
- ".pushsection .init.data,\"aw\"\n\t"
- ".align " __ASM_SEL(4, 8) "\n\t"
- ".type int3_selftest_ip, @object\n\t"
- ".size int3_selftest_ip, " __ASM_SEL(4, 8) "\n\t"
- "int3_selftest_ip:\n\t"
- __ASM_SEL(.long, .quad) " 1b\n\t"
- ".popsection\n\t"
+ asm volatile ("int3_selftest_ip: int3; nop; nop; nop; nop\n\t"
: ASM_CALL_CONSTRAINT
: __ASM_SEL_RAW(a, D) (&val)
: "memory");
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