riscv: kprobes: Fix probe address validation

When adding a kprobe such as "p:probe/tcp_sendmsg _text+15392192",
arch_check_kprobe would start iterating all instructions starting from
_text until the probed address. Not only is this very inefficient, but
literal values in there (e.g. left by function patching) are
misinterpreted in a way that causes a desync.

Fix this by doing it like x86: start the iteration at the closest
preceding symbol instead of the given starting point.

Fixes: 87f48c7 ("riscv: kprobe: Fixup kernel panic when probing an illegal position")
Signed-off-by: Fabian Vogt <fvogt@suse.de>
Signed-off-by: Marvin Friedrich <marvin.friedrich@suse.com>
Acked-by: Guo Ren <guoren@kernel.org>
Link: https://lore.kernel.org/r/6191817.lOV4Wx5bFT@fvogt-thinkpad
Signed-off-by: Paul Walmsley <pjw@kernel.org>

Author: Vogtinator

arch/riscv/kernel/probes/kprobes.c

@@ -49,10 +49,15 @@ static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
 	post_kprobe_handler(p, kcb, regs);
 }
 
-static bool __kprobes arch_check_kprobe(struct kprobe *p)
+static bool __kprobes arch_check_kprobe(unsigned long addr)
 {
-	unsigned long tmp  = (unsigned long)p->addr - p->offset;
-	unsigned long addr = (unsigned long)p->addr;
+	unsigned long tmp, offset;
+
+	/* start iterating at the closest preceding symbol */
+	if (!kallsyms_lookup_size_offset(addr, NULL, &offset))
+		return false;
+
+	tmp = addr - offset;
 
 	while (tmp <= addr) {
 		if (tmp == addr)
@@ -71,7 +76,7 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 	if ((unsigned long)insn & 0x1)
 		return -EILSEQ;
 
-	if (!arch_check_kprobe(p))
+	if (!arch_check_kprobe((unsigned long)p->addr))
 		return -EILSEQ;
 
 	/* copy instruction */