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Supervisor Mode Access Prevention (SMAP) is an x86 CPU feature that prevents the kernel from accessing userspace memory. With SMAP enabled, trying to read/write a userspace memory address while in the kernel will now generate a page fault. Since it's sometimes necessary to read/write userspace memory, there are two new instructions that quickly switch the protection on/off: STAC (disables protection) and CLAC (enables protection.) These are exposed in kernel code via the stac() and clac() helpers. There's also a SmapDisabler RAII object that can be used to ensure that you don't forget to re-enable protection before returning to userspace code. THis patch also adds copy_to_user(), copy_from_user() and memset_user() which are the "correct" way of doing things. These functions allow us to briefly disable protection for a specific purpose, and then turn it back on immediately after it's done. Going forward all kernel code should be moved to using these and all uses of SmapDisabler are to be considered FIXME's. Note that we're not realizing the full potential of this feature since I've used SmapDisabler quite liberally in this initial bring-up patch.
29 lines
851 B
C
29 lines
851 B
C
#pragma once
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#include <AK/Types.h>
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extern "C" {
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static_assert(sizeof(size_t) == 4);
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void* copy_to_user(void*, const void*, size_t);
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void* copy_from_user(void*, const void*, size_t);
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void* memset_user(void*, int, size_t);
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void* memcpy(void*, const void*, size_t);
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char* strcpy(char*, const char*);
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char* strncpy(char*, const char*, size_t);
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int strncmp(const char* s1, const char* s2, size_t n);
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int strcmp(char const*, const char*);
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size_t strlen(const char*);
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size_t strnlen(const char*, size_t);
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void* memset(void*, int, size_t);
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char* strdup(const char*);
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int memcmp(const void*, const void*, size_t);
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char* strrchr(const char* str, int ch);
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void* memmove(void* dest, const void* src, size_t n);
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inline u16 ntohs(u16 w) { return (w & 0xff) << 8 | ((w >> 8) & 0xff); }
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inline u16 htons(u16 w) { return (w & 0xff) << 8 | ((w >> 8) & 0xff); }
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}
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