diff mbox series

[03/17] mm: add generic __va_function and __pa_function macros

Message ID 20210312004919.669614-4-samitolvanen@google.com (mailing list archive)
State New
Headers show
Series Add support for Clang CFI | expand

Commit Message

Sami Tolvanen March 12, 2021, 12:49 a.m. UTC
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>
---
 include/linux/mm.h | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

Kees Cook March 12, 2021, 2:40 a.m. UTC | #1
On Thu, Mar 11, 2021 at 04:49:05PM -0800, Sami Tolvanen wrote:
> 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>
diff mbox series

Patch

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 77e64e3eac80..1262c4c0242c 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