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Date: Fri, 3 Jan 2020 12:39:48 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>
Cc: Ard Biesheuvel <ardb@...nel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
Arvind Sankar <nivedita@...m.mit.edu>,
Matthew Garrett <mjg59@...gle.com>
Subject: [PATCH 15/20] efi/x86: Check number of arguments to variadic functions
From: Arvind Sankar <nivedita@...m.mit.edu>
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@...m.mit.edu>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
arch/x86/boot/compressed/efi_thunk_64.S | 4 +-
arch/x86/include/asm/efi.h | 54 ++++++++++++++++++++++++-
arch/x86/platform/efi/efi_stub_64.S | 4 +-
arch/x86/platform/efi/efi_thunk_64.S | 4 +-
4 files changed, 58 insertions(+), 8 deletions(-)
diff --git a/arch/x86/boot/compressed/efi_thunk_64.S b/arch/x86/boot/compressed/efi_thunk_64.S
index 6d95eb6b8912..d040ff5458e5 100644
--- a/arch/x86/boot/compressed/efi_thunk_64.S
+++ b/arch/x86/boot/compressed/efi_thunk_64.S
@@ -23,7 +23,7 @@
.code64
.text
-SYM_FUNC_START(efi64_thunk)
+SYM_FUNC_START(__efi64_thunk)
push %rbp
push %rbx
@@ -95,7 +95,7 @@ SYM_FUNC_START(efi64_thunk)
pop %rbx
pop %rbp
ret
-SYM_FUNC_END(efi64_thunk)
+SYM_FUNC_END(__efi64_thunk)
.code32
/*
diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index e7e9c6e057f9..cfc450085584 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)
{
diff --git a/arch/x86/platform/efi/efi_stub_64.S b/arch/x86/platform/efi/efi_stub_64.S
index e7e1020f4ccb..15da118f04f0 100644
--- a/arch/x86/platform/efi/efi_stub_64.S
+++ b/arch/x86/platform/efi/efi_stub_64.S
@@ -10,7 +10,7 @@
#include <linux/linkage.h>
#include <asm/nospec-branch.h>
-SYM_FUNC_START(efi_call)
+SYM_FUNC_START(__efi_call)
pushq %rbp
movq %rsp, %rbp
and $~0xf, %rsp
@@ -24,4 +24,4 @@ SYM_FUNC_START(efi_call)
CALL_NOSPEC %rdi
leave
ret
-SYM_FUNC_END(efi_call)
+SYM_FUNC_END(__efi_call)
diff --git a/arch/x86/platform/efi/efi_thunk_64.S b/arch/x86/platform/efi/efi_thunk_64.S
index 162b35729633..26f0da238c1c 100644
--- a/arch/x86/platform/efi/efi_thunk_64.S
+++ b/arch/x86/platform/efi/efi_thunk_64.S
@@ -25,7 +25,7 @@
.text
.code64
-SYM_CODE_START(efi64_thunk)
+SYM_CODE_START(__efi64_thunk)
push %rbp
push %rbx
@@ -69,4 +69,4 @@ SYM_CODE_START(efi64_thunk)
2: pushl $__KERNEL_CS
pushl %ebp
lret
-SYM_CODE_END(efi64_thunk)
+SYM_CODE_END(__efi64_thunk)
--
2.20.1
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