x86/ibt,kprobes: Cure sym+0 equals fentry woes

In order to allow kprobes to skip the ENDBR instructions at sym+0 for
X86_KERNEL_IBT builds, change _kprobe_addr() to take an architecture
callback to inspect the function at hand and modify the offset if
needed.

This streamlines the existing interface to cover more cases and
require less hooks. Once PowerPC gets fully converted there will only
be the one arch hook.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.405947704@infradead.org

1 files changed, 21 insertions, 13 deletions

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 9a492fdec1df..7dae0b01abfb 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -105,6 +105,27 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
 	return addr;
 }
 
+static bool arch_kprobe_on_func_entry(unsigned long offset)
+{
+#ifdef PPC64_ELF_ABI_v2
+#ifdef CONFIG_KPROBES_ON_FTRACE
+	return offset <= 16;
+#else
+	return offset <= 8;
+#endif
+#else
+	return !offset;
+#endif
+}
+
+/* XXX try and fold the magic of kprobe_lookup_name() in this */
+kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
+					 bool *on_func_entry)
+{
+	*on_func_entry = arch_kprobe_on_func_entry(offset);
+	return (kprobe_opcode_t *)(addr + offset);
+}
+
 void *alloc_insn_page(void)
 {
 	void *page;
@@ -218,19 +239,6 @@ static nokprobe_inline void set_current_kprobe(struct kprobe *p, struct pt_regs
 	kcb->kprobe_saved_msr = regs->msr;
 }
 
-bool arch_kprobe_on_func_entry(unsigned long offset)
-{
-#ifdef PPC64_ELF_ABI_v2
-#ifdef CONFIG_KPROBES_ON_FTRACE
-	return offset <= 16;
-#else
-	return offset <= 8;
-#endif
-#else
-	return !offset;
-#endif
-}
-
 void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
 {
 	ri->ret_addr = (kprobe_opcode_t *)regs->link;