linux-kernel - [PATCH] ARM: kprobes: Fix false positive with FORTIFY

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Message-ID: <20181022093023.GA8920@beast>
Date:   Mon, 22 Oct 2018 02:30:23 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Russell King <linux@...linux.org.uk>
Cc:     William Cohen <wcohen@...hat.com>,
        Laura Abbott <labbott@...hat.com>,
        linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH] ARM: kprobes: Fix false positive with FORTIFY_SOURCE

The arm compiler internally interprets an inline assembly label
as an unsigned long value, not a pointer. As a result, under
CONFIG_FORTIFY_SOURCE, the size of the array pointed to by an address
of a label is 4 bytes, which was tripping the runtime checks. Instead,
we can just cast the label (as done with the size calculations earlier)
to avoid the problem.

Reported-by: William Cohen <wcohen@...hat.com>
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Cc: stable@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/arm/probes/kprobes/opt-arm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/probes/kprobes/opt-arm.c b/arch/arm/probes/kprobes/opt-arm.c
index b2aa9b32bff2..2c118a6ab358 100644
--- a/arch/arm/probes/kprobes/opt-arm.c
+++ b/arch/arm/probes/kprobes/opt-arm.c
@@ -247,7 +247,7 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *or
 	}
 
 	/* Copy arch-dep-instance from template. */
-	memcpy(code, &optprobe_template_entry,
+	memcpy(code, (unsigned char *)optprobe_template_entry,
 			TMPL_END_IDX * sizeof(kprobe_opcode_t));
 
 	/* Adjust buffer according to instruction. */
-- 
2.17.1


-- 
Kees Cook
Pixel Security