[PATCH v3 02/10] x86/ibt: Add exact_endbr() helper

Peter Zijlstra
2025-02-19T16:36:52Z

For when we want to exactly match ENDBR, and not everything that we
can scribble it with.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kernel/alternative.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -863,6 +863,17 @@ __noendbr bool is_endbr(u32 *val)
return false;
}

+static __noendbr bool exact_endbr(u32 *val)
+{
+ u32 endbr;
+
+ __get_kernel_nofault(&endbr, val, u32, Efault);
+ return endbr == gen_endbr();
+
+Efault:
+ return false;
+}
+
static void poison_cfi(void *addr);

static void __init_or_module poison_endbr(void *addr)
@@ -1427,10 +1438,9 @@ static void poison_cfi(void *addr)
bool decode_fineibt_insn(struct pt_regs *regs, unsigned long *target, u32 *type)
{
unsigned long addr = regs->ip - fineibt_preamble_ud2;
- u32 endbr, hash;
+ u32 hash;

- __get_kernel_nofault(&endbr, addr, u32, Efault);
- if (endbr != gen_endbr())
+ if (!exact_endbr((void *)addr))
return false;

*target = addr + fineibt_preamble_size;