On Thu, Apr 01, 2021 at 04:32:01PM -0700, 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 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 <samitolvanen@xxxxxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> FWIW: Acked-by: Mark Rutland <mark.rutland@xxxxxxx> Mark. > --- > 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. > -- > 2.31.0.208.g409f899ff0-goog >
