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From: Ard Biesheuvel <ardb@kernel.org>
To: linux-efi@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Matthew Garrett <mjg59@google.com>
Subject: [PATCH 15/20] efi/x86: Check number of arguments to variadic functions
Date: Fri,  3 Jan 2020 12:39:48 +0100
Message-ID: <20200103113953.9571-16-ardb@kernel.org> (raw)
In-Reply-To: <20200103113953.9571-1-ardb@kernel.org>

From: Arvind Sankar <nivedita@alum.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@alum.mit.edu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.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


  parent reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-03 11:39 [GIT PULL 00/20] More EFI updates for v5.6 Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 01/20] efi/libstub: fix boot argument handling in mixed mode entry code Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 02/20] efi/libstub/x86: force 'hidden' visibility for extern declarations Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 03/20] efi/x86: re-disable RT services for 32-bit kernels running on 64-bit EFI Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 04/20] efi/x86: map the entire EFI vendor string before copying it Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 05/20] efi/x86: avoid redundant cast of EFI firmware service pointer Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 06/20] efi/x86: split off some old memmap handling into separate routines Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 07/20] efi/x86: split SetVirtualAddresMap() wrappers into 32 and 64 bit versions Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 08/20] efi/x86: simplify i386 efi_call_phys() firmware call wrapper Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 09/20] efi/x86: simplify 64-bit EFI " Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 10/20] efi/x86: simplify mixed mode " Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 11/20] efi/x86: drop two near identical versions of efi_runtime_init() Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 12/20] efi/x86: clean up efi_systab_init() routine for legibility Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 13/20] efi/x86: don't panic or BUG() on non-critical error conditions Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 14/20] efi/x86: remove unreachable code in kexec_enter_virtual_mode() Ard Biesheuvel
2020-01-03 11:39 ` Ard Biesheuvel [this message]
2020-01-03 11:39 ` [PATCH 16/20] efi/x86: Allow translating 64-bit arguments for mixed mode calls Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 17/20] efi: Allow disabling PCI busmastering on bridges during boot Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 18/20] x86/mm: fix NX bit clearing issue in kernel_map_pages_in_pgd Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 19/20] efi/x86: don't map the entire kernel text RW for mixed mode Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 20/20] efi/x86: avoid RWX mappings for all of DRAM Ard Biesheuvel
2020-01-09  9:37 ` [GIT PULL 00/20] More EFI updates for v5.6 Ard Biesheuvel
2020-01-10 18:13   ` Ingo Molnar
2020-01-13  7:29     ` Ard Biesheuvel

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