Re: [PATCH v4] mm/alloc_tag: Fix panic when CONFIG_KASAN enabled and CONFIG_KASAN_VMALLOC not enabled

[Suren Baghdasaryan]

On Wed, Dec 11, 2024 at 5:38 PM Hao Ge <hao.ge@xxxxxxxxx> wrote:
>
> From: Hao Ge <gehao@xxxxxxxxxx>
>
> 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.

nit: the above wording is a bit unclear. Instead of module_tags I
would call it "memory for module allocation tags". So, I would change
the above paragraph to:

The memory for module allocation tags is allocated on demand,
therefore we need to allocate shadow memory on demand as well in
MODULE_ALIGN blocks.

>
> 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@xxxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/1ba0cc57-e2ed-caa2-1241-aa5615bee01f@xxxxxxxxxxxxxxx/
> Suggested-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Signed-off-by: Hao Ge <gehao@xxxxxxxxxx>

Other than that nit, LGTM.

Acked-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>

> ---
> v4: Based on Suren's suggestion for modification (to make the code simpler),
>     modify the code.
>     Update the comments in the code due to the modifications made to the code.
>     Add Suggested-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
>
> 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 | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> index f942408b53ef..c5bdfa297a35 100644
> --- a/lib/alloc_tag.c
> +++ b/lib/alloc_tag.c
> @@ -407,6 +407,8 @@ static int vm_module_tags_populate(void)
>
>         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;
>
> @@ -421,7 +423,19 @@ static int vm_module_tags_populate(void)
>                                 __free_page(next_page[i]);
>                         return -ENOMEM;
>                 }
> +
>                 vm_module_tags->nr_pages += nr;
> +
> +               /*
> +                * 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.
> +                */
> +               if (old_shadow_end < new_shadow_end)
> +                       kasan_alloc_module_shadow((void *)old_shadow_end,
> +                                                 new_shadow_end - old_shadow_end,
> +                                                 GFP_KERNEL);
>         }
>
>         /*
> --
> 2.25.1
>