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arm64: mte: handle tags zeroing at page allocation time

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Currently, on an anonymous page fault, the kernel allocates a zeroed
page and maps it in user space. If the mapping is tagged (PROT_MTE),
set_pte_at() additionally clears the tags. It is, however, more
efficient to clear the tags at the same time as zeroing the data on
allocation. To avoid clearing the tags on any page (which may not be
mapped as tagged), only do this if the vma flags contain VM_MTE. This
requires introducing a new GFP flag that is used to determine whether
to clear the tags.

The DC GZVA instruction with a 0 top byte (and 0 tag) requires
top-byte-ignore. Set the TCR_EL1.{TBI1,TBID1} bits irrespective of
whether KASAN_HW is enabled.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Co-developed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://linux-review.googlesource.com/id/Id46dc94e30fe11474f7e54f5d65e7658dbdddb26
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://lore.kernel.org/r/20210602235230.3928842-4-pcc@google.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Peter Collingbourne 2021-06-02 16:52:29 -07:00 committed by Will Deacon
parent 7a3b835371
commit 013bb59dbb
9 changed files with 96 additions and 11 deletions
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4
arch/arm64/include/asm/mte.h
View File

@ -37,6 +37,7 @@ void mte_free_tag_storage(char *storage);
/* track which pages have valid allocation tags */
#define PG_mte_tagged PG_arch_2
void mte_zero_clear_page_tags(void *addr);
void mte_sync_tags(pte_t *ptep, pte_t pte);
void mte_copy_page_tags(void *kto, const void *kfrom);
void mte_thread_init_user(void);
@ -53,6 +54,9 @@ int mte_ptrace_copy_tags(struct task_struct *child, long request,
/* unused if !CONFIG_ARM64_MTE, silence the compiler */
#define PG_mte_tagged 0
static inline void mte_zero_clear_page_tags(void *addr)
{
}
static inline void mte_sync_tags(pte_t *ptep, pte_t pte)
{
}

8
arch/arm64/include/asm/page.h
View File

@ -13,6 +13,7 @@
#ifndef __ASSEMBLY__
#include <linux/personality.h> /* for READ_IMPLIES_EXEC */
#include <linux/types.h> /* for gfp_t */
#include <asm/pgtable-types.h>
struct page;
@ -28,10 +29,13 @@ void copy_user_highpage(struct page *to, struct page *from,
void copy_highpage(struct page *to, struct page *from);
#define __HAVE_ARCH_COPY_HIGHPAGE
#define alloc_zeroed_user_highpage_movable(vma, vaddr) \
alloc_page_vma(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, vma, vaddr)
struct page *alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma,
unsigned long vaddr);
#define __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE_MOVABLE
void tag_clear_highpage(struct page *to);
#define __HAVE_ARCH_TAG_CLEAR_HIGHPAGE
#define clear_user_page(page, vaddr, pg) clear_page(page)
#define copy_user_page(to, from, vaddr, pg) copy_page(to, from)

20
arch/arm64/lib/mte.S
View File

@ -36,6 +36,26 @@ SYM_FUNC_START(mte_clear_page_tags)
ret
SYM_FUNC_END(mte_clear_page_tags)
/*
* Zero the page and tags at the same time
*
* Parameters:
* x0 - address to the beginning of the page
*/
SYM_FUNC_START(mte_zero_clear_page_tags)
mrs x1, dczid_el0
and w1, w1, #0xf
mov x2, #4
lsl x1, x2, x1
and x0, x0, #(1 << MTE_TAG_SHIFT) - 1 // clear the tag
1: dc gzva, x0
add x0, x0, x1
tst x0, #(PAGE_SIZE - 1)
b.ne 1b
ret
SYM_FUNC_END(mte_zero_clear_page_tags)
/*
* Copy the tags from the source page to the destination one
* x0 - address of the destination page

26
arch/arm64/mm/fault.c
View File

@ -921,3 +921,29 @@ void do_debug_exception(unsigned long addr_if_watchpoint, unsigned int esr,
debug_exception_exit(regs);
}
NOKPROBE_SYMBOL(do_debug_exception);
/*
* Used during anonymous page fault handling.
*/
struct page *alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma,
unsigned long vaddr)
{
gfp_t flags = GFP_HIGHUSER_MOVABLE | __GFP_ZERO;
/*
* If the page is mapped with PROT_MTE, initialise the tags at the
* point of allocation and page zeroing as this is usually faster than
* separate DC ZVA and STGM.
*/
if (vma->vm_flags & VM_MTE)
flags |= __GFP_ZEROTAGS;
return alloc_page_vma(flags, vma, vaddr);
}
void tag_clear_highpage(struct page *page)
{
mte_zero_clear_page_tags(page_address(page));
page_kasan_tag_reset(page);
set_bit(PG_mte_tagged, &page->flags);
}

10
arch/arm64/mm/proc.S
View File

@ -46,9 +46,13 @@
#endif
#ifdef CONFIG_KASAN_HW_TAGS
#define TCR_KASAN_HW_FLAGS SYS_TCR_EL1_TCMA1 | TCR_TBI1 | TCR_TBID1
#define TCR_MTE_FLAGS SYS_TCR_EL1_TCMA1 | TCR_TBI1 | TCR_TBID1
#else
#define TCR_KASAN_HW_FLAGS 0
/*
* The mte_zero_clear_page_tags() implementation uses DC GZVA, which relies on
* TBI being enabled at EL1.
*/
#define TCR_MTE_FLAGS TCR_TBI1 | TCR_TBID1
#endif
/*
@ -464,7 +468,7 @@ SYM_FUNC_START(__cpu_setup)
msr_s SYS_TFSRE0_EL1, xzr
/* set the TCR_EL1 bits */
mov_q x10, TCR_KASAN_HW_FLAGS
mov_q x10, TCR_MTE_FLAGS
orr tcr, tcr, x10
1:
#endif

9
include/linux/gfp.h
View File

@ -53,8 +53,9 @@ struct vm_area_struct;
#define ___GFP_HARDWALL 0x100000u
#define ___GFP_THISNODE 0x200000u
#define ___GFP_ACCOUNT 0x400000u
#define ___GFP_ZEROTAGS 0x800000u
#ifdef CONFIG_LOCKDEP
#define ___GFP_NOLOCKDEP 0x800000u
#define ___GFP_NOLOCKDEP 0x1000000u
#else
#define ___GFP_NOLOCKDEP 0
#endif
@ -229,16 +230,20 @@ struct vm_area_struct;
* %__GFP_COMP address compound page metadata.
*
* %__GFP_ZERO returns a zeroed page on success.
*
* %__GFP_ZEROTAGS returns a page with zeroed memory tags on success, if
* __GFP_ZERO is set.
*/
#define __GFP_NOWARN ((__force gfp_t)___GFP_NOWARN)
#define __GFP_COMP ((__force gfp_t)___GFP_COMP)
#define __GFP_ZERO ((__force gfp_t)___GFP_ZERO)
#define __GFP_ZEROTAGS ((__force gfp_t)___GFP_ZEROTAGS)
/* Disable lockdep for GFP context tracking */
#define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
/* Room for N __GFP_FOO bits */
#define __GFP_BITS_SHIFT (23 + IS_ENABLED(CONFIG_LOCKDEP))
#define __GFP_BITS_SHIFT (24 + IS_ENABLED(CONFIG_LOCKDEP))
#define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
/**

8
include/linux/highmem.h
View File

@ -185,6 +185,14 @@ static inline void clear_highpage(struct page *page)
kunmap_atomic(kaddr);
}
#ifndef __HAVE_ARCH_TAG_CLEAR_HIGHPAGE
static inline void tag_clear_highpage(struct page *page)
{
}
#endif
/*
* If we pass in a base or tail page, we can zero up to PAGE_SIZE.
* If we pass in a head page, we can zero up to the size of the compound page.

9
mm/kasan/hw_tags.c
View File

@ -246,7 +246,14 @@ void kasan_alloc_pages(struct page *page, unsigned int order, gfp_t flags)
*/
bool init = !want_init_on_free() && want_init_on_alloc(flags);
kasan_unpoison_pages(page, order, init);
if (flags & __GFP_ZEROTAGS) {
int i;
for (i = 0; i != 1 << order; ++i)
tag_clear_highpage(page + i);
} else {
kasan_unpoison_pages(page, order, init);
}
}
void kasan_free_pages(struct page *page, unsigned int order)

13
mm/page_alloc.c
View File

@ -1219,10 +1219,16 @@ out:
return ret;
}
static void kernel_init_free_pages(struct page *page, int numpages)
static void kernel_init_free_pages(struct page *page, int numpages, bool zero_tags)
{
int i;
if (zero_tags) {
for (i = 0; i < numpages; i++)
tag_clear_highpage(page + i);
return;
}
/* s390's use of memset() could override KASAN redzones. */
kasan_disable_current();
for (i = 0; i < numpages; i++) {
@ -1314,7 +1320,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
bool init = want_init_on_free();
if (init)
kernel_init_free_pages(page, 1 << order);
kernel_init_free_pages(page, 1 << order, false);
if (!skip_kasan_poison)
kasan_poison_pages(page, order, init);
}
@ -2349,7 +2355,8 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
kasan_unpoison_pages(page, order, init);
if (init)
kernel_init_free_pages(page, 1 << order);
kernel_init_free_pages(page, 1 << order,
gfp_flags & __GFP_ZEROTAGS);
}
set_page_owner(page, order, gfp_flags);