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https://github.com/acidanthera/audk.git
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e6b6aa90d4
Adds dynamic stack cookies in the form of copies of the entry point libraries that use shared logic to update stack cookies at runtime. This relies on RDRAND on IA32/X64 and RNDR on AARCH64 to get a random number to apply to the stack cookie on module entry point. This simplifies the logic a platform must do to include stack check functionality. Signed-off-by: Oliver Smith-Denny <osde@microsoft.com>
64 lines
2.2 KiB
NASM
64 lines
2.2 KiB
NASM
;------------------------------------------------------------------------------
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;
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; Copyright (c) Microsoft Corporation.
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; SPDX-License-Identifier: BSD-2-Clause-Patent
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;
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; Module Name:
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;
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; DynamicCookie.nasm
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;
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; Abstract:
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;
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; Generates random number through CPU RdRand instruction on a 32-bit platform
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; to store a random value in the GCC __stack_check_guard stack cookie.
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; The first byte is 0'd to prevent string copy functions from clobbering
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; the stack cookie.
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;
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; Notes:
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;
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; If RdRand fails, the build time static stack cookie value will be used instead.
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;
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;------------------------------------------------------------------------------
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SECTION .text
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extern ASM_PFX(__stack_chk_guard)
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extern ASM_PFX(_CModuleEntryPoint)
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global ASM_PFX(_ModuleEntryPoint)
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;------------------------------------------------------------------------------
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; VOID
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; EFIAPI
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; _ModuleEntryPoint (
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; Parameters are passed through
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; );
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;------------------------------------------------------------------------------
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global _ModuleEntryPoint
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_ModuleEntryPoint:
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push ebx
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push ecx
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push edx
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mov eax, 1 ; CPUID function 1
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cpuid
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test ecx, 0x40000000 ; Check if the RdRand bit (bit 30) is set in ECX
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jz c_entry ; If not set, jump to c_entry
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rdrand eax ; Use rdrand, getting a 32 bit value as on
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; IA32, __stack_chk_guard is a 32 bit value.
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; CF=1 if RN generated ok, otherwise CF=0
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jnc c_entry ; If the cmd fails, don't update __stack_chk_guard, we'll have to move forward
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; with the static value provided at build time.
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lea ebx, [ASM_PFX(__stack_chk_guard)] ; load the address of __stack_chk_guard into ebx
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xor ah, ah ; Zero a byte of the __stack_chk_guard value to protect against string functions
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; (such as strcpy like functions) clobbering past the canary
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mov [ebx], eax ; Store our random value, with 0'd first byte to __stack_chk_guard
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c_entry:
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pop edx
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pop ecx
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pop ebx
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jmp ASM_PFX(_CModuleEntryPoint)
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