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McKenney" , Christoph Hellwig , Peter Zijlstra , Sedat Dilek , 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210331_222731_397577_E145F6C2 X-CRM114-Status: GOOD ( 15.06 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org With CONFIG_CFI_CLANG, the compiler replaces function addresses in instrumented C code with jump table addresses. This means that __pa_symbol(function) returns the physical address of the jump table entry instead of the actual function, which may not work as the jump table code will immediately jump to a virtual address that may not be mapped. To avoid this address space confusion, this change adds a generic definition for function_nocfi(), which architectures that support CFI can override. The typical implementation of would use inline assembly to take the function address, which avoids compiler instrumentation. Signed-off-by: Sami Tolvanen Reviewed-by: Kees Cook --- include/linux/mm.h | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index 8ba434287387..22cce9c7dd05 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -124,6 +124,16 @@ extern int mmap_rnd_compat_bits __read_mostly; #define lm_alias(x) __va(__pa_symbol(x)) #endif +/* + * With CONFIG_CFI_CLANG, the compiler replaces function addresses in + * instrumented C code with jump table addresses. Architectures that + * support CFI can define this macro to return the actual function address + * when needed. + */ +#ifndef function_nocfi +#define function_nocfi(x) (x) +#endif + /* * To prevent common memory management code establishing * a zero page mapping on a read fault.