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kasan/arm64: improve comments for KASAN_SHADOW_START/END 

Patch series "kasan: assorted clean-ups".

Code clean-ups, nothing worthy of being backported to stable.


This patch (of 11):

Unify and improve the comments for KASAN_SHADOW_START/END definitions from
include/asm/kasan.h and include/asm/memory.h.

Also put both definitions together in include/asm/memory.h.

Also clarify the related BUILD_BUG_ON checks in mm/kasan_init.c.

Link: https://lkml.kernel.org/r/cover.1703188911.git.andreyknvl@google.com
Link: https://lkml.kernel.org/r/140108ca0b164648c395a41fbeecb0601b1ae9e1.1703188911.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Andrey Konovalov 2023-12-21 21:04:43 +01:00 committed by Andrew Morton
parent 51fb591edc
commit 27232ba96c
3 changed files with 39 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
arch/arm64/include/asm/kasan.h
View File

@ -15,29 +15,9 @@
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
void kasan_init(void);
/*
* KASAN_SHADOW_START: beginning of the kernel virtual addresses.
* KASAN_SHADOW_END: KASAN_SHADOW_START + 1/N of kernel virtual addresses,
* where N = (1 << KASAN_SHADOW_SCALE_SHIFT).
*
* KASAN_SHADOW_OFFSET:
* This value is used to map an address to the corresponding shadow
* address by the following formula:
* shadow_addr = (address >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET
*
* (1 << (64 - KASAN_SHADOW_SCALE_SHIFT)) shadow addresses that lie in range
* [KASAN_SHADOW_OFFSET, KASAN_SHADOW_END) cover all 64-bits of virtual
* addresses. So KASAN_SHADOW_OFFSET should satisfy the following equation:
* KASAN_SHADOW_OFFSET = KASAN_SHADOW_END -
* (1ULL << (64 - KASAN_SHADOW_SCALE_SHIFT))
*/
#define _KASAN_SHADOW_START(va) (KASAN_SHADOW_END - (1UL << ((va) - KASAN_SHADOW_SCALE_SHIFT)))
#define KASAN_SHADOW_START _KASAN_SHADOW_START(vabits_actual)
void kasan_copy_shadow(pgd_t *pgdir);
asmlinkage void kasan_early_init(void);
void kasan_init(void);
void kasan_copy_shadow(pgd_t *pgdir);
#else
static inline void kasan_init(void) { }

38
arch/arm64/include/asm/memory.h
View File

@ -65,15 +65,41 @@
#define KERNEL_END _end
/*
* Generic and tag-based KASAN require 1/8th and 1/16th of the kernel virtual
* address space for the shadow region respectively. They can bloat the stack
* significantly, so double the (minimum) stack size when they are in use.
* Generic and Software Tag-Based KASAN modes require 1/8th and 1/16th of the
* kernel virtual address space for storing the shadow memory respectively.
*
* The mapping between a virtual memory address and its corresponding shadow
* memory address is defined based on the formula:
*
* shadow_addr = (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET
*
* where KASAN_SHADOW_SCALE_SHIFT is the order of the number of bits that map
* to a single shadow byte and KASAN_SHADOW_OFFSET is a constant that offsets
* the mapping. Note that KASAN_SHADOW_OFFSET does not point to the start of
* the shadow memory region.
*
* Based on this mapping, we define two constants:
*
* KASAN_SHADOW_START: the start of the shadow memory region;
* KASAN_SHADOW_END: the end of the shadow memory region.
*
* KASAN_SHADOW_END is defined first as the shadow address that corresponds to
* the upper bound of possible virtual kernel memory addresses UL(1) << 64
* according to the mapping formula.
*
* KASAN_SHADOW_START is defined second based on KASAN_SHADOW_END. The shadow
* memory start must map to the lowest possible kernel virtual memory address
* and thus it depends on the actual bitness of the address space.
*
* As KASAN inserts redzones between stack variables, this increases the stack
* memory usage significantly. Thus, we double the (minimum) stack size.
*/
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
#define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
#define KASAN_SHADOW_END ((UL(1) << (64 - KASAN_SHADOW_SCALE_SHIFT)) \
+ KASAN_SHADOW_OFFSET)
#define PAGE_END (KASAN_SHADOW_END - (1UL << (vabits_actual - KASAN_SHADOW_SCALE_SHIFT)))
#define KASAN_SHADOW_END ((UL(1) << (64 - KASAN_SHADOW_SCALE_SHIFT)) + KASAN_SHADOW_OFFSET)
#define _KASAN_SHADOW_START(va) (KASAN_SHADOW_END - (UL(1) << ((va) - KASAN_SHADOW_SCALE_SHIFT)))
#define KASAN_SHADOW_START _KASAN_SHADOW_START(vabits_actual)
#define PAGE_END KASAN_SHADOW_START
#define KASAN_THREAD_SHIFT 1
#else
#define KASAN_THREAD_SHIFT 0

5
arch/arm64/mm/kasan_init.c
View File

@ -170,6 +170,11 @@ asmlinkage void __init kasan_early_init(void)
{
BUILD_BUG_ON(KASAN_SHADOW_OFFSET !=
KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT)));
/*
* We cannot check the actual value of KASAN_SHADOW_START during build,
* as it depends on vabits_actual. As a best-effort approach, check
* potential values calculated based on VA_BITS and VA_BITS_MIN.
*/
BUILD_BUG_ON(!IS_ALIGNED(_KASAN_SHADOW_START(VA_BITS), PGDIR_SIZE));
BUILD_BUG_ON(!IS_ALIGNED(_KASAN_SHADOW_START(VA_BITS_MIN), PGDIR_SIZE));
BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE));