arm64: add __nocfi to functions that jump to a physical address

Disable CFI checking for functions that switch to linear mapping and
make an indirect call to a physical address, since the compiler only
understands virtual addresses and the CFI check for such indirect calls
would always fail.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-15-samitolvanen@google.com

arch/arm64/include/asm/mmu_context.h

@@ -119,7 +119,7 @@ static inline void cpu_install_idmap(void)
  * Atomically replaces the active TTBR1_EL1 PGD with a new VA-compatible PGD,
  * avoiding the possibility of conflicting TLB entries being allocated.
  */
-static inline void cpu_replace_ttbr1(pgd_t *pgdp)
+static inline void __nocfi cpu_replace_ttbr1(pgd_t *pgdp)
 {
 	typedef void (ttbr_replace_func)(phys_addr_t);
 	extern ttbr_replace_func idmap_cpu_replace_ttbr1;

arch/arm64/kernel/cpu-reset.h

@@ -13,7 +13,7 @@
 void __cpu_soft_restart(unsigned long el2_switch, unsigned long entry,
 	unsigned long arg0, unsigned long arg1, unsigned long arg2);
 
-static inline void __noreturn cpu_soft_restart(unsigned long entry,
+static inline void __noreturn __nocfi cpu_soft_restart(unsigned long entry,
 						       unsigned long arg0,
 						       unsigned long arg1,
 						       unsigned long arg2)

arch/arm64/kernel/cpufeature.c

@@ -1445,7 +1445,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 }
 
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
-static void
+static void __nocfi
 kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused)
 {
 	typedef void (kpti_remap_fn)(int, int, phys_addr_t);