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Date:   Tue, 23 Mar 2021 13:39:32 -0700
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Subject: [PATCH v3 03/17] mm: add generic __va_function and __pa_function macros
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>, 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,
        Sami Tolvanen <samitolvanen@google.com>
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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 generic
definitions for __va_function and __pa_function, which architectures
that support CFI can override. The typical implementation of the
__va_function macro would use inline assembly to take the function
address, which avoids compiler instrumentation.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 include/linux/mm.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 64a71bf20536..a0d285cd59ce 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -116,6 +116,14 @@ extern int mmap_rnd_compat_bits __read_mostly;
 #define __pa_symbol(x)  __pa(RELOC_HIDE((unsigned long)(x), 0))
 #endif
 
+#ifndef __va_function
+#define __va_function(x) (x)
+#endif
+
+#ifndef __pa_function
+#define __pa_function(x) __pa_symbol(__va_function(x))
+#endif
+
 #ifndef page_to_virt
 #define page_to_virt(x)	__va(PFN_PHYS(page_to_pfn(x)))
 #endif
-- 
2.31.0.291.g576ba9dcdaf-goog