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Message-ID: <20220224151322.892372059@infradead.org>
User-Agent: quilt/0.66
Date:   Thu, 24 Feb 2022 15:51:53 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     x86@kernel.org, joao@overdrivepizza.com, hjl.tools@gmail.com,
        jpoimboe@redhat.com, andrew.cooper3@citrix.com
Cc:     linux-kernel@vger.kernel.org, peterz@infradead.org,
        ndesaulniers@google.com, keescook@chromium.org,
        samitolvanen@google.com, mark.rutland@arm.com,
        alyssa.milburn@intel.com, mbenes@suse.cz, rostedt@goodmis.org,
        mhiramat@kernel.org, alexei.starovoitov@gmail.com
Subject: [PATCH v2 15/39] x86/ibt,kprobes: Fix more +0 assumptions
References: <20220224145138.952963315@infradead.org>
MIME-Version: 1.0
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Precedence: bulk

With IBT on, sym+0 is no longer the __fentry__ site.

NOTE: the architecture has a special case and *does* allow placing an
INT3 breakpoint over ENDBR in which case #BP has precedence over #CP
and as such we don't need to disallow probing these instructions.

NOTE: irrespective of the above; there is a complication in that
direct branches to functions are rewritten to not execute ENDBR, so
any breakpoint thereon might miss lots of actual function executions.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/kernel/kprobes/core.c |   11 +++++++++++
 kernel/kprobes.c               |   15 ++++++++++++---
 2 files changed, 23 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1156,3 +1162,8 @@ int arch_trampoline_kprobe(struct kprobe
 {
 	return 0;
 }
+
+bool arch_kprobe_on_func_entry(unsigned long offset)
+{
+	return offset <= 4*HAS_KERNEL_IBT;
+}
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -67,10 +67,19 @@ static bool kprobes_all_disarmed;
 static DEFINE_MUTEX(kprobe_mutex);
 static DEFINE_PER_CPU(struct kprobe *, kprobe_instance);
 
-kprobe_opcode_t * __weak kprobe_lookup_name(const char *name,
-					unsigned int __unused)
+kprobe_opcode_t * __weak kprobe_lookup_name(const char *name, unsigned int offset)
 {
-	return ((kprobe_opcode_t *)(kallsyms_lookup_name(name)));
+	kprobe_opcode_t *addr = NULL;
+
+	addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)));
+#ifdef CONFIG_KPROBES_ON_FTRACE
+	if (addr && !offset) {
+		unsigned long faddr = ftrace_location((unsigned long)addr);
+		if (faddr)
+			addr = (kprobe_opcode_t *)faddr;
+	}
+#endif
+	return addr;
 }
 
 /*