Re: [PATCH v3] mm/alloc_tag: Fix panic when CONFIG_KASAN enabled and CONFIG_KASAN_VMALLOC not enabled

Hao Ge
2024-12-12T01:08:21Z

Hi Suren

On 12/12/24 00:32, Suren Baghdasaryan wrote:
> On Tue, Dec 10, 2024 at 6:58 PM Hao Ge <hao.ge@linux.dev> wrote:
>> From: Hao Ge <gehao@kylinos.cn>
>>
>> When CONFIG_KASAN is enabled but CONFIG_KASAN_VMALLOC
>> is not enabled, we may encounter a panic during system boot.
>>
>> Because we haven't allocated pages and created mappings
>> for the shadow memory corresponding to module_tags region,
>> similar to how it is done for execmem_vmalloc.
>>
>> The difference is that our module_tags are allocated on demand,
>> so similarly,we also need to allocate shadow memory regions on demand.
>> However, we still need to adhere to the MODULE_ALIGN principle.
>>
>> Here is the log for panic:
>>
>> [ 18.349421] BUG: unable to handle page fault for address: fffffbfff8092000
>> [ 18.350016] #PF: supervisor read access in kernel mode
>> [ 18.350459] #PF: error_code(0x0000) - not-present page
>> [ 18.350904] PGD 20fe52067 P4D 219dc8067 PUD 219dc4067 PMD 102495067 PTE 0
>> [ 18.351484] Oops: Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI
>> [ 18.351961] CPU: 5 UID: 0 PID: 1 Comm: systemd Not tainted 6.13.0-rc1+ #3
>> [ 18.352533] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
>> [ 18.353494] RIP: 0010:kasan_check_range+0xba/0x1b0
>> [ 18.353931] Code: 8d 5a 07 4c 0f 49 da 49 c1 fb 03 45 85 db 0f 84 dd 00 00 00 45 89 db 4a 8d 14 d8 eb 0d 48 83 c0 08 48 39 c2 0f 84 c1 00 00 00 <48> 83 38 00 74 ed 48 8d 50 08 eb 0d 48 83 c0 01 48 39 d0 0f 84 90
>> [ 18.355484] RSP: 0018:ff11000101877958 EFLAGS: 00010206
>> [ 18.355937] RAX: fffffbfff8092000 RBX: fffffbfff809201e RCX: ffffffff82a7ceac
>> [ 18.356542] RDX: fffffbfff8092018 RSI: 00000000000000f0 RDI: ffffffffc0490000
>> [ 18.357153] RBP: fffffbfff8092000 R08: 0000000000000001 R09: fffffbfff809201d
>> [ 18.357756] R10: ffffffffc04900ef R11: 0000000000000003 R12: ffffffffc0490000
>> [ 18.358365] R13: ff11000101877b48 R14: ffffffffc0490000 R15: 000000000000002c
>> [ 18.358968] FS: 00007f9bd13c5940(0000) GS:ff110001eb480000(0000) knlGS:0000000000000000
>> [ 18.359648] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 18.360178] CR2: fffffbfff8092000 CR3: 0000000109214004 CR4: 0000000000771ef0
>> [ 18.360790] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> [ 18.361404] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> [ 18.362020] PKRU: 55555554
>> [ 18.362261] Call Trace:
>> [ 18.362481] <TASK>
>> [ 18.362671] ? __die+0x23/0x70
>> [ 18.362964] ? page_fault_oops+0xc2/0x160
>> [ 18.363318] ? exc_page_fault+0xad/0xc0
>> [ 18.363680] ? asm_exc_page_fault+0x26/0x30
>> [ 18.364056] ? move_module+0x3cc/0x8a0
>> [ 18.364398] ? kasan_check_range+0xba/0x1b0
>> [ 18.364755] __asan_memcpy+0x3c/0x60
>> [ 18.365074] move_module+0x3cc/0x8a0
>> [ 18.365386] layout_and_allocate.constprop.0+0x3d5/0x720
>> [ 18.365841] ? early_mod_check+0x3dc/0x510
>> [ 18.366195] load_module+0x72/0x1850
>> [ 18.366509] ? __pfx_kernel_read_file+0x10/0x10
>> [ 18.366918] ? vm_mmap_pgoff+0x21c/0x2d0
>> [ 18.367262] init_module_from_file+0xd1/0x130
>> [ 18.367638] ? __pfx_init_module_from_file+0x10/0x10
>> [ 18.368073] ? __pfx__raw_spin_lock+0x10/0x10
>> [ 18.368456] ? __pfx_cred_has_capability.isra.0+0x10/0x10
>> [ 18.368938] idempotent_init_module+0x22c/0x790
>> [ 18.369332] ? simple_getattr+0x6f/0x120
>> [ 18.369676] ? __pfx_idempotent_init_module+0x10/0x10
>> [ 18.370110] ? fdget+0x58/0x3a0
>> [ 18.370393] ? security_capable+0x64/0xf0
>> [ 18.370745] __x64_sys_finit_module+0xc2/0x140
>> [ 18.371136] do_syscall_64+0x7d/0x160
>> [ 18.371459] ? fdget_pos+0x1c8/0x4c0
>> [ 18.371784] ? ksys_read+0xfd/0x1d0
>> [ 18.372106] ? syscall_exit_to_user_mode+0x10/0x1f0
>> [ 18.372525] ? do_syscall_64+0x89/0x160
>> [ 18.372860] ? do_syscall_64+0x89/0x160
>> [ 18.373194] ? do_syscall_64+0x89/0x160
>> [ 18.373527] ? syscall_exit_to_user_mode+0x10/0x1f0
>> [ 18.373952] ? do_syscall_64+0x89/0x160
>> [ 18.374283] ? syscall_exit_to_user_mode+0x10/0x1f0
>> [ 18.374701] ? do_syscall_64+0x89/0x160
>> [ 18.375037] ? do_user_addr_fault+0x4a8/0xa40
>> [ 18.375416] ? clear_bhb_loop+0x25/0x80
>> [ 18.375748] ? clear_bhb_loop+0x25/0x80
>> [ 18.376119] ? clear_bhb_loop+0x25/0x80
>> [ 18.376450] entry_SYSCALL_64_after_hwframe+0x76/0x7e
>>
>> Fixes: 233e89322cbe ("alloc_tag: fix module allocation tags populated area calculation")
>> Reported-by: Ben Greear <greearb@candelatech.com>
>> Closes: https://lore.kernel.org/all/1ba0cc57-e2ed-caa2-1241-aa5615bee01f@candelatech.com/
>> Signed-off-by: Hao Ge <gehao@kylinos.cn>
>> ---
>> v3: Adjusting the title because the previous one was a bit unclear.
>> Suren has pointed out that our condition for determining whether
>> to allocate shadow memory is unreasonable.We have adjusted our method
>> to use every 8 pages as an index (idx), and we will make decisions based
>> on this idx when determining whether to allocate shadow memory.
>>
>> v2: Add comments to facilitate understanding of the code.
>> Add align nr << PAGE_SHIFT to MODULE_ALIGN,even though kasan_alloc_module_shadow
>> already handles this internally,but to make the code more readable and user-friendly
>>
>> commit 233e89322cbe ("alloc_tag: fix module allocation
>> tags populated area calculation") is currently in the
>> mm-hotfixes-unstable branch, so this patch is
>> developed based on the mm-hotfixes-unstable branch.
>> ---
>> lib/alloc_tag.c | 23 +++++++++++++++++++++++
>> 1 file changed, 23 insertions(+)
>>
>> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
>> index f942408b53ef..8bf04756887d 100644
>> --- a/lib/alloc_tag.c
>> +++ b/lib/alloc_tag.c
>> @@ -10,6 +10,7 @@
>> #include <linux/seq_buf.h>
>> #include <linux/seq_file.h>
>> #include <linux/vmalloc.h>
>> +#include <linux/math.h>
>>
>> #define ALLOCINFO_FILE_NAME "allocinfo"
>> #define MODULE_ALLOC_TAG_VMAP_SIZE (100000UL * sizeof(struct alloc_tag))
>> @@ -404,6 +405,9 @@ static int vm_module_tags_populate(void)
>> unsigned long phys_end = ALIGN_DOWN(module_tags.start_addr, PAGE_SIZE) +
>> (vm_module_tags->nr_pages << PAGE_SHIFT);
>> unsigned long new_end = module_tags.start_addr + module_tags.size;
>> + unsigned long phys_idx = (vm_module_tags->nr_pages +
>> + (2 << KASAN_SHADOW_SCALE_SHIFT) - 1) >> KASAN_SHADOW_SCALE_SHIFT;
>> + unsigned long new_idx = 0;
>>
>> if (phys_end < new_end) {
>> struct page **next_page = vm_module_tags->pages + vm_module_tags->nr_pages;
>> @@ -421,7 +425,26 @@ static int vm_module_tags_populate(void)
>> __free_page(next_page[i]);
>> return -ENOMEM;
>> }
>> +
>> vm_module_tags->nr_pages += nr;
>> +
>> + new_idx = (vm_module_tags->nr_pages +
>> + (2 << KASAN_SHADOW_SCALE_SHIFT) - 1) >> KASAN_SHADOW_SCALE_SHIFT;
>> +
>> + /*
>> + * Kasan allocates 1 byte of shadow for every 8 bytes of data.
>> + * When kasan_alloc_module_shadow allocates shadow memory,
>> + * its unit of allocation is a page.
>> + * Therefore, here we need to align to MODULE_ALIGN.
>> + *
>> + * For every KASAN_SHADOW_SCALE_SHIFT, a shadow page is allocated.
>> + * So, we determine whether to allocate based on whether the
>> + * number of pages falls within the scope of the same KASAN_SHADOW_SCALE_SHIFT.
>> + */
>> + if (phys_idx != new_idx)
>> + kasan_alloc_module_shadow((void *)round_up(phys_end, MODULE_ALIGN),
>> + (new_idx - phys_idx) * MODULE_ALIGN,
>> + GFP_KERNEL);
>> }
> This seems overly-complicated. I was thinking something like this would work:
>
> static int vm_module_tags_populate(void)
> {
> unsigned long phys_end = ALIGN_DOWN(module_tags.start_addr, PAGE_SIZE) +
> (vm_module_tags->nr_pages << PAGE_SHIFT);
> unsigned long new_end = module_tags.start_addr + module_tags.size;
>
> if (phys_end < new_end) {
> struct page **next_page = vm_module_tags->pages +
> vm_module_tags->nr_pages;
> + unsigned long old_shadow_end = ALIGN(phys_end, MODULE_ALIGN);
> + unsigned long new_shadow_end = ALIGN(new_end, MODULE_ALIGN);
> unsigned long more_pages;
> unsigned long nr;
>
> more_pages = ALIGN(new_end - phys_end, PAGE_SIZE) >> PAGE_SHIFT;
> nr = alloc_pages_bulk_array_node(GFP_KERNEL | __GFP_NOWARN,
> NUMA_NO_NODE,
> more_pages, next_page);
> if (nr < more_pages ||
> vmap_pages_range(phys_end, phys_end + (nr <<
> PAGE_SHIFT), PAGE_KERNEL,
> next_page, PAGE_SHIFT) < 0) {
> /* Clean up and error out */
> for (int i = 0; i < nr; i++)
> __free_page(next_page[i]);
> return -ENOMEM;
> }
> vm_module_tags->nr_pages += nr;
> + if (old_shadow_end < new_shadow_end)
> + kasan_alloc_module_shadow((void *)old_shadow_end,
> + new_shadow_end - old_shadow_end
> + GFP_KERNEL);
> }
>
> WDYT?

Yes, it's much simpler this way.

I'll verify for accuracy,If there are no issues, I'll release the V4
version and add your "Suggested-by".

Thanks

Best Regards

Hao

>
>> /*
>> --
>> 2.25.1
>>