The shadow's page table is not updated when PTE_RPN_SHIFT is 24
and PAGE_SHIFT is 12. It not only causes false positives but
also false negative as shown the following text.
Fix it by bringing the logic of kasan_early_shadow_page_entry here.
1. False Positive:
==================================================================
BUG: KASAN: vmalloc-out-of-bounds in pcpu_alloc+0x508/0xa50
Write of size 16 at addr f57f3be0 by task swapper/0/1
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.15.0-12267-gdebe436e77c7 #1
Call Trace:
[c80d1c20] [c07fe7b8] dump_stack_lvl+0x4c/0x6c (unreliable)
[c80d1c40] [c02ff668] print_address_description.constprop.0+0x88/0x300
[c80d1c70] [c02ff45c] kasan_report+0x1ec/0x200
[c80d1cb0] [c0300b20] kasan_check_range+0x160/0x2f0
[c80d1cc0] [c03018a4] memset+0x34/0x90
[c80d1ce0] [c0280108] pcpu_alloc+0x508/0xa50
[c80d1d40] [c02fd7bc] __kmem_cache_create+0xfc/0x570
[c80d1d70] [c0283d64] kmem_cache_create_usercopy+0x274/0x3e0
[c80d1db0] [c2036580] init_sd+0xc4/0x1d0
[c80d1de0] [c00044a0] do_one_initcall+0xc0/0x33c
[c80d1eb0] [c2001624] kernel_init_freeable+0x2c8/0x384
[c80d1ef0] [c0004b14] kernel_init+0x24/0x170
[c80d1f10] [c001b26c] ret_from_kernel_thread+0x5c/0x64
Memory state around the buggy address:
f57f3a80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
f57f3b00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>f57f3b80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
^
f57f3c00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
f57f3c80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
==================================================================
2. False Negative (with KASAN tests):
==================================================================
Before fix:
ok 45 - kmalloc_double_kzfree
# vmalloc_oob: EXPECTATION FAILED at lib/test_kasan.c:1039
KASAN failure expected in "((volatile char *)area)[3100]", but none occurred
not ok 46 - vmalloc_oob
not ok 1 - kasan
==================================================================
After fix:
ok 1 - kasan
Fixes: cbd18991e24fe ("powerpc/mm: Fix an Oops in kasan_mmu_init()")
Cc: [email protected] # 5.4.x
Signed-off-by: Chen Jingwen <[email protected]>
---
arch/powerpc/mm/kasan/kasan_init_32.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c b/arch/powerpc/mm/kasan/kasan_init_32.c
index cf8770b1a692e..f3e4d069e0ba7 100644
--- a/arch/powerpc/mm/kasan/kasan_init_32.c
+++ b/arch/powerpc/mm/kasan/kasan_init_32.c
@@ -83,13 +83,12 @@ void __init
kasan_update_early_region(unsigned long k_start, unsigned long k_end, pte_t pte)
{
unsigned long k_cur;
- phys_addr_t pa = __pa(kasan_early_shadow_page);
for (k_cur = k_start; k_cur != k_end; k_cur += PAGE_SIZE) {
pmd_t *pmd = pmd_off_k(k_cur);
pte_t *ptep = pte_offset_kernel(pmd, k_cur);
- if ((pte_val(*ptep) & PTE_RPN_MASK) != pa)
+ if (pte_page(*ptep) != virt_to_page(lm_alias(kasan_early_shadow_page)))
continue;
__set_pte_at(&init_mm, k_cur, ptep, pte, 0);
--
2.19.1
Le 29/12/2021 à 04:52, Chen Jingwen a écrit :
> The shadow's page table is not updated when PTE_RPN_SHIFT is 24
> and PAGE_SHIFT is 12. It not only causes false positives but
> also false negative as shown the following text.
>
> Fix it by bringing the logic of kasan_early_shadow_page_entry here.
>
> 1. False Positive:
> ==================================================================
> BUG: KASAN: vmalloc-out-of-bounds in pcpu_alloc+0x508/0xa50
> Write of size 16 at addr f57f3be0 by task swapper/0/1
>
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.15.0-12267-gdebe436e77c7 #1
> Call Trace:
> [c80d1c20] [c07fe7b8] dump_stack_lvl+0x4c/0x6c (unreliable)
> [c80d1c40] [c02ff668] print_address_description.constprop.0+0x88/0x300
> [c80d1c70] [c02ff45c] kasan_report+0x1ec/0x200
> [c80d1cb0] [c0300b20] kasan_check_range+0x160/0x2f0
> [c80d1cc0] [c03018a4] memset+0x34/0x90
> [c80d1ce0] [c0280108] pcpu_alloc+0x508/0xa50
> [c80d1d40] [c02fd7bc] __kmem_cache_create+0xfc/0x570
> [c80d1d70] [c0283d64] kmem_cache_create_usercopy+0x274/0x3e0
> [c80d1db0] [c2036580] init_sd+0xc4/0x1d0
> [c80d1de0] [c00044a0] do_one_initcall+0xc0/0x33c
> [c80d1eb0] [c2001624] kernel_init_freeable+0x2c8/0x384
> [c80d1ef0] [c0004b14] kernel_init+0x24/0x170
> [c80d1f10] [c001b26c] ret_from_kernel_thread+0x5c/0x64
>
> Memory state around the buggy address:
> f57f3a80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> f57f3b00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>> f57f3b80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> ^
> f57f3c00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> f57f3c80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
> ==================================================================
>
> 2. False Negative (with KASAN tests):
> ==================================================================
> Before fix:
> ok 45 - kmalloc_double_kzfree
> # vmalloc_oob: EXPECTATION FAILED at lib/test_kasan.c:1039
> KASAN failure expected in "((volatile char *)area)[3100]", but none occurred
> not ok 46 - vmalloc_oob
> not ok 1 - kasan
>
> ==================================================================
> After fix:
> ok 1 - kasan
>
> Fixes: cbd18991e24fe ("powerpc/mm: Fix an Oops in kasan_mmu_init()")
> Cc: [email protected] # 5.4.x
> Signed-off-by: Chen Jingwen <[email protected]>
Reviewed-by: Christophe Leroy <[email protected]>
> ---
> arch/powerpc/mm/kasan/kasan_init_32.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c b/arch/powerpc/mm/kasan/kasan_init_32.c
> index cf8770b1a692e..f3e4d069e0ba7 100644
> --- a/arch/powerpc/mm/kasan/kasan_init_32.c
> +++ b/arch/powerpc/mm/kasan/kasan_init_32.c
> @@ -83,13 +83,12 @@ void __init
> kasan_update_early_region(unsigned long k_start, unsigned long k_end, pte_t pte)
> {
> unsigned long k_cur;
> - phys_addr_t pa = __pa(kasan_early_shadow_page);
>
> for (k_cur = k_start; k_cur != k_end; k_cur += PAGE_SIZE) {
> pmd_t *pmd = pmd_off_k(k_cur);
> pte_t *ptep = pte_offset_kernel(pmd, k_cur);
>
> - if ((pte_val(*ptep) & PTE_RPN_MASK) != pa)
> + if (pte_page(*ptep) != virt_to_page(lm_alias(kasan_early_shadow_page)))
> continue;
>
> __set_pte_at(&init_mm, k_cur, ptep, pte, 0);
On Wed, 29 Dec 2021 11:52:26 +0800, Chen Jingwen wrote:
> The shadow's page table is not updated when PTE_RPN_SHIFT is 24
> and PAGE_SHIFT is 12. It not only causes false positives but
> also false negative as shown the following text.
>
> Fix it by bringing the logic of kasan_early_shadow_page_entry here.
>
> 1. False Positive:
> ==================================================================
> BUG: KASAN: vmalloc-out-of-bounds in pcpu_alloc+0x508/0xa50
> Write of size 16 at addr f57f3be0 by task swapper/0/1
>
> [...]
Applied to powerpc/next.
[1/1] powerpc/kasan: Fix early region not updated correctly
https://git.kernel.org/powerpc/c/dd75080aa8409ce10d50fb58981c6b59bf8707d3
cheers