efi/x86: Check number of arguments to variadic functions
On x86 we need to thunk through assembler stubs to call the EFI services
for mixed mode, and for runtime services in 64-bit mode. The assembler
stubs have limits on how many arguments it handles. Introduce a few
macros to check that we do not try to pass too many arguments to the
stubs.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Matthew Garrett <mjg59@google.com>
Cc: linux-efi@vger.kernel.org
Link: https://lkml.kernel.org/r/20200103113953.9571-16-ardb@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index e7e9c6e..cfc4500 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -8,6 +8,7 @@
#include <asm/tlb.h>
#include <asm/nospec-branch.h>
#include <asm/mmu_context.h>
+#include <linux/build_bug.h>
/*
* We map the EFI regions needed for runtime services non-contiguously,
@@ -34,6 +35,45 @@
#define ARCH_EFI_IRQ_FLAGS_MASK X86_EFLAGS_IF
+/*
+ * The EFI services are called through variadic functions in many cases. These
+ * functions are implemented in assembler and support only a fixed number of
+ * arguments. The macros below allows us to check at build time that we don't
+ * try to call them with too many arguments.
+ *
+ * __efi_nargs() will return the number of arguments if it is 7 or less, and
+ * cause a BUILD_BUG otherwise. The limitations of the C preprocessor make it
+ * impossible to calculate the exact number of arguments beyond some
+ * pre-defined limit. The maximum number of arguments currently supported by
+ * any of the thunks is 7, so this is good enough for now and can be extended
+ * in the obvious way if we ever need more.
+ */
+
+#define __efi_nargs(...) __efi_nargs_(__VA_ARGS__)
+#define __efi_nargs_(...) __efi_nargs__(0, ##__VA_ARGS__, \
+ __efi_arg_sentinel(7), __efi_arg_sentinel(6), \
+ __efi_arg_sentinel(5), __efi_arg_sentinel(4), \
+ __efi_arg_sentinel(3), __efi_arg_sentinel(2), \
+ __efi_arg_sentinel(1), __efi_arg_sentinel(0))
+#define __efi_nargs__(_0, _1, _2, _3, _4, _5, _6, _7, n, ...) \
+ __take_second_arg(n, \
+ ({ BUILD_BUG_ON_MSG(1, "__efi_nargs limit exceeded"); 8; }))
+#define __efi_arg_sentinel(n) , n
+
+/*
+ * __efi_nargs_check(f, n, ...) will cause a BUILD_BUG if the ellipsis
+ * represents more than n arguments.
+ */
+
+#define __efi_nargs_check(f, n, ...) \
+ __efi_nargs_check_(f, __efi_nargs(__VA_ARGS__), n)
+#define __efi_nargs_check_(f, p, n) __efi_nargs_check__(f, p, n)
+#define __efi_nargs_check__(f, p, n) ({ \
+ BUILD_BUG_ON_MSG( \
+ (p) > (n), \
+ #f " called with too many arguments (" #p ">" #n ")"); \
+})
+
#ifdef CONFIG_X86_32
#define arch_efi_call_virt_setup() \
({ \
@@ -56,7 +96,12 @@
#define EFI_LOADER_SIGNATURE "EL64"
-extern asmlinkage u64 efi_call(void *fp, ...);
+extern asmlinkage u64 __efi_call(void *fp, ...);
+
+#define efi_call(...) ({ \
+ __efi_nargs_check(efi_call, 7, __VA_ARGS__); \
+ __efi_call(__VA_ARGS__); \
+})
/*
* struct efi_scratch - Scratch space used while switching to/from efi_mm
@@ -139,7 +184,12 @@ struct efi_setup_data {
extern u64 efi_setup;
#ifdef CONFIG_EFI
-extern efi_status_t efi64_thunk(u32, ...);
+extern efi_status_t __efi64_thunk(u32, ...);
+
+#define efi64_thunk(...) ({ \
+ __efi_nargs_check(efi64_thunk, 6, __VA_ARGS__); \
+ __efi64_thunk(__VA_ARGS__); \
+})
static inline bool efi_is_mixed(void)
{