linux-kernel - Re: [PATCH RESEND] kprobes: be more permissive when user specifies both symbol name and address

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Date:	Tue, 29 Jul 2014 20:47:38 +0800
From:	Jianyu Zhan <nasa4836@...il.com>
To:	mingo@...nel.org
Cc:	masami.hiramatsu.pt@...achi.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jianyu Zhan <nasa4836@...il.com>
Subject: Re: [PATCH RESEND] kprobes: be more permissive when user specifies both symbol  name and address

Hi, Ingo,

Here is the new patch with typo fixed.

Thanks.

---8<---

Currently, if user specifies both symbol name and address, we just
bail out.

This might be too rude. This patch makes it give more tolerance.
If both are specified, check address first, if the symbol found
does not match the one user specify, print a waring. If not found,
return -ENOENT, because some symbols might have muplitple instances,
we don't bother to check symbol name.
---
 Documentation/kprobes.txt |  4 +++-
 kernel/kprobes.c          | 32 +++++++++++++++++++++++++++++---
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index 4bbeca8..663b5ad 100644
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -358,7 +358,9 @@ to install a probepoint is known. This field is used to calculate the
 probepoint.
 
 3. Specify either the kprobe "symbol_name" OR the "addr". If both are
-specified, kprobe registration will fail with -EINVAL.
+specified, only check "addr", because some symbols might have multiple
+instances. If neither is specified, kprobe registration will fail
+with -EINVAL.
 
 4. With CISC architectures (such as i386 and x86_64), the kprobes code
 does not validate if the kprobe.addr is at an instruction boundary.
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 734e9a7..9768608 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1358,15 +1358,41 @@ static bool within_kprobe_blacklist(unsigned long addr)
 static kprobe_opcode_t *kprobe_addr(struct kprobe *p)
 {
 	kprobe_opcode_t *addr = p->addr;
+	char namebuf[KSYM_NAME_LEN];
+	const char *sym_name = NULL;
+	unsigned long offset;
 
-	if ((p->symbol_name && p->addr) ||
-	    (!p->symbol_name && !p->addr))
+	if (!p->symbol_name && !p->addr)
 		goto invalid;
 
-	if (p->symbol_name) {
+	/*
+	 * Some symbols might have multiple instances,
+	 * so if both are specified, only check address.
+	 */
+	if (unlikely(p->addr && p->symbol_name)) {
+		sym_name = kallsyms_lookup((unsigned long)(p->addr),
+				NULL, &offset, NULL, namebuf);
+		if (!sym_name)
+			return ERR_PTR(-ENOENT);
+
+		if (strncmp(sym_name, p->symbol_name, KSYM_NAME_LEN)
+				|| offset != p->offset) {
+			pr_err("Incorrect symbol or offset, should be "
+				"symbol=%s, offset=%ld.\n", sym_name, offset);
+			goto invalid;
+		}
+	} else if (p->symbol_name) {
+		/* Only symbol case */
 		kprobe_lookup_name(p->symbol_name, addr);
 		if (!addr)
 			return ERR_PTR(-ENOENT);
+	} else {
+		/*
+		 * Only address case.
+		 * Since we later will do a sanity check of the
+		 * address range in check_kprobe_address_safe(),
+		 * do nothing here.
+		 */
 	}
 
 	addr = (kprobe_opcode_t *)(((char *)addr) + p->offset);
-- 
2.0.0

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