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kmsan: Add a comment explaining why KMSAN doesn't shadow above KERNBASE

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Sponsored by:	The FreeBSD Foundation
This commit is contained in:
Mark Johnston 2023-07-15 14:04:55 -04:00
parent 96c2538121
commit 640e5cb304
1 changed files with 9 additions and 2 deletions
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11
sys/amd64/include/msan.h
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@ -41,8 +41,9 @@
typedef uint32_t msan_orig_t;
/*
* Our 32-bit origin cells encode a 2-bit type and 30-bit pointer. The pointer
* is compressed by making it a positive offset relative to KERNBASE.
* Our 32-bit origin cells encode a 2-bit type and 30-bit pointer to a kernel
* instruction. The pointer is compressed by making it a positive offset
* relative to KERNBASE.
*/
#define KMSAN_ORIG_TYPE_SHIFT 30u
#define KMSAN_ORIG_PTR_MASK ((1u << KMSAN_ORIG_TYPE_SHIFT) - 1)
@ -76,6 +77,12 @@ kmsan_md_addr_to_orig(vm_offset_t addr)
static inline bool
kmsan_md_unsupported(vm_offset_t addr)
{
/*
* The kernel itself isn't shadowed: for most purposes global variables
* are always initialized, and because KMSAN kernels are large
* (GENERIC-KMSAN is ~80MB at the time of writing), shadowing would
* incur signficant memory usage.
*/
return (addr < VM_MIN_KERNEL_ADDRESS || addr >= KERNBASE);
}