Re: [PATCH v2] mm/alloc_tag: Add kasan_alloc_module_shadow when CONFIS_KASAN_VMALLOC disabled

Suren Baghdasaryan
2024-12-10T17:55:39Z

On Mon, Dec 9, 2024 at 10:53 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>
> ---
> 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 | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> index f942408b53ef..bd3ee57ea13f 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))
> @@ -422,6 +423,17 @@ static int vm_module_tags_populate(void)
> 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,
> + * it does so in units of pages.
> + * Therefore, here we need to align to MODULE_ALIGN.
> + */
> + if ((phys_end & (MODULE_ALIGN - 1)) == 0)

phys_end is calculated as:

unsigned long phys_end = ALIGN_DOWN(module_tags.start_addr, PAGE_SIZE) +
(vm_module_tags->nr_pages
<< PAGE_SHIFT);

and therefore is always PAGE_SIZE-aligned. PAGE_SIZE is always a
multiple of MODULE_ALIGN, therefore phys_end is always
MODULE_ALIGN-aligned and the above condition is not needed.

> + kasan_alloc_module_shadow((void *)phys_end,
> + round_up(nr << PAGE_SHIFT, MODULE_ALIGN),

Here again, (nr << PAGE_SHIFT) is PAGE_SIZE-aligned and PAGE_SIZE is a
multiple of MODULE_ALIGN, therefore (nr << PAGE_SHIFT) is always
multiple of MODULE_ALIGN and there is no need for round_up().

IOW, I think this patch should simply add one line:

vm_module_tags->nr_pages += nr;
+ kasan_alloc_module_shadow((void *)phys_end, nr <<
PAGE_SHIFT, GFP_KERNEL);

Am I missing something?

> + GFP_KERNEL);
> }
>
> /*
> --
> 2.25.1
>