[PATCH v6 12/18] arm64: implement function_nocfi

From: Sami Tolvanen <samitolvanen@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Will Deacon <will@kernel.org>, Jessica Yu <jeyu@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>, Tejun Heo <tj@kernel.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Christoph Hellwig <hch@infradead.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	bpf@vger.kernel.org, linux-hardening@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kbuild@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
	Sami Tolvanen <samitolvanen@google.com>
Subject: [PATCH v6 12/18] arm64: implement function_nocfi
Date: Thu,  8 Apr 2021 11:28:37 -0700	[thread overview]
Message-ID: <20210408182843.1754385-13-samitolvanen@google.com> (raw)
In-Reply-To: <20210408182843.1754385-1-samitolvanen@google.com>

With CONFIG_CFI_CLANG, the compiler replaces function addresses in
instrumented C code with jump table addresses. This change implements
the function_nocfi() macro, which returns the actual function address
instead.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/arm64/include/asm/memory.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 0aabc3be9a75..3a6f9df63606 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -321,6 +321,22 @@ static inline void *phys_to_virt(phys_addr_t x)
 #define virt_to_pfn(x)		__phys_to_pfn(__virt_to_phys((unsigned long)(x)))
 #define sym_to_pfn(x)		__phys_to_pfn(__pa_symbol(x))
 
+#ifdef CONFIG_CFI_CLANG
+/*
+ * With CONFIG_CFI_CLANG, the compiler replaces function address
+ * references with the address of the function's CFI jump table
+ * entry. The function_nocfi macro always returns the address of the
+ * actual function instead.
+ */
+#define function_nocfi(x) ({						\
+	void *addr;							\
+	asm("adrp %0, " __stringify(x) "\n\t"				\
+	    "add  %0, %0, :lo12:" __stringify(x)			\
+	    : "=r" (addr));						\
+	addr;								\
+})
+#endif
+
 /*
  *  virt_to_page(x)	convert a _valid_ virtual address to struct page *
  *  virt_addr_valid(x)	indicates whether a virtual address is valid
-- 
2.31.1.295.g9ea45b61b8-goog

