linux-kernel - [PATCH 4.13 32/36] powerpc/kprobes: Dereference function pointers only if the address does not belong to kernel text

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Message-Id: <20171106085048.478153980@linuxfoundation.org>
Date:   Mon,  6 Nov 2017 10:12:45 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 4.13 32/36] powerpc/kprobes: Dereference function pointers only if the address does not belong to kernel text

4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>

commit e6c4dcb308160115287afd87afb63b5684d75a5b upstream.

This makes the changes introduced in commit 83e840c770f2c5
("powerpc64/elfv1: Only dereference function descriptor for non-text
symbols") to be specific to the kprobe subsystem.

We previously changed ppc_function_entry() to always check the provided
address to confirm if it needed to be dereferenced. This is actually
only an issue for kprobe blacklisted asm labels (through use of
_ASM_NOKPROBE_SYMBOL) and can cause other issues with ftrace. Also, the
additional checks are not really necessary for our other uses.

As such, move this check to the kprobes subsystem.

Fixes: 83e840c770f2 ("powerpc64/elfv1: Only dereference function descriptor for non-text symbols")
Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/powerpc/kernel/kprobes.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -600,7 +600,12 @@ NOKPROBE_SYMBOL(kprobe_fault_handler);

 unsigned long arch_deref_entry_point(void *entry)
 {
-	return ppc_global_function_entry(entry);
+#ifdef PPC64_ELF_ABI_v1
+	if (!kernel_text_address((unsigned long)entry))
+		return ppc_global_function_entry(entry);
+	else
+#endif
+		return (unsigned long)entry;
 }
 NOKPROBE_SYMBOL(arch_deref_entry_point);