[PATCH v3] arm64: mm: fix pass user prot to ioremap_prot in generic_access_phys

[Jinjiang Tu]

在 2026/2/3 17:23, Will Deacon 写道:
> On Tue, Feb 03, 2026 at 11:38:15AM +0800, Jinjiang Tu wrote:
>> 在 2026/2/2 22:55, Will Deacon 写道:
>>> On Fri, Jan 30, 2026 at 03:38:07PM +0800, Jinjiang Tu wrote:
>>>> Here is a syzkaller error log:
>>>>     [0000000020ffc000] pgd=080000010598d403, p4d=080000010598d403, pud=0800000125ddb403,
>>>>                        pmd=080000007833c403, pte=01608000007fcfcf
>>>>     Unable to handle kernel read from unreadable memory at virtual address ffff80008ea89000
>>>>     KASAN: probably user-memory-access in range [0x0000000475448000-0x0000000475448007]
>>>>     Mem abort info:
>>>>       ESR = 0x000000009600000f
>>>>       EC = 0x25: DABT (current EL), IL = 32 bits
>>>>       SET = 0, FnV = 0
>>>>       EA = 0, S1PTW = 0
>>>>       FSC = 0x0f: level 3 permission fault
>>>>     Data abort info:
>>>>       ISV = 0, ISS = 0x0000000f, ISS2 = 0x00000000
>>>>       CM = 0, WnR = 0, TnD = 0, TagAccess = 0
>>>>       GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
>>>>     swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000001244aa000
>>>>     [ffff80008ea89000] pgd=100000013ffff403, p4d=100000013ffff403, pud=100000013fffe403,
>>>> 		     pmd=100000010a453403, pte=01608000007fcfcf
>>>>     Internal error: Oops: 000000009600000f [#1] SMP
>>>>     Modules linked in: team
>>>>     CPU: 1 PID: 10840 Comm: syz.9.83 Kdump: loaded Tainted: G
>>>>     Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
>>>>     pstate: 20400005 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>>>>     pc : __memcpy_fromio+0x80/0xf8
>>>>     lr : generic_access_phys+0x20c/0x2b8
>>>>     sp : ffff8000a0507960
>>>>     x29: ffff8000a0507960 x28: 1ffff000140a0f44 x27: ffff00003833cfe0
>>>>     x26: 0000000000000000 x25: 0000000000001000 x24: 0010000000000001
>>>>     x23: ffff80008ea89000 x22: ffff00004ea63000 x21: 0000000000001000
>>>>     x20: ffff80008ea89000 x19: ffff00004ea62000 x18: 0000000000000000
>>>>     x17: 0000000000000000 x16: 0000000000000000 x15: ffff8000806f1e3c
>>>>     x14: ffff8000806f1d44 x13: 0000000041b58ab3 x12: ffff7000140a0f23
>>>>     x11: 1ffff000140a0f22 x10: ffff7000140a0f22 x9 : ffff800080579d24
>>>>     x8 : 0000000000000004 x7 : 0000000000000003 x6 : 0000000000000001
>>>>     x5 : ffff8000a0507910 x4 : ffff7000140a0f22 x3 : dfff800000000000
>>>>     x2 : 0000000000001000 x1 : ffff80008ea89000 x0 : ffff00004ea62000
>>>>     Call trace:
>>>>       __memcpy_fromio+0x80/0xf8
>>>>       generic_access_phys+0x20c/0x2b8
>>>>       __access_remote_vm+0x46c/0x5b8
>>>>       access_remote_vm+0x18/0x30
>>>>       environ_read+0x238/0x3e8
>>>>       vfs_read+0xe4/0x2b0
>>>>       ksys_read+0xcc/0x178
>>>>       __arm64_sys_read+0x4c/0x68
>>>>       invoke_syscall+0x68/0x1a0
>>>>       el0_svc_common.constprop.0+0x11c/0x150
>>>>       do_el0_svc+0x38/0x50
>>>>       el0_svc+0x50/0x258
>>>>       el0t_64_sync_handler+0xc0/0xc8
>>>>       el0t_64_sync+0x1a4/0x1a8
>>>>     Code: 91002339 aa1403f7 8b190276 d503201f (f94002f8)
>>>>
>>>> The local syzkaller first maps I/O address from /dev/mem to userspace,
>>>> overiding the stack vma with MAP_FIXED flag. As a result, when reading
>>>> /proc/$pid/environ, generic_access_phys() is called to access the region,
>>>> which triggers a PAN permission-check fault and causes a kernel access
>>>> fault.
>>>>
>>>> The root cause is that generic_access_phys() passes a user pte to
>>>> ioremap_prot(), the user pte sets PTE_USER and PTE_NG bits.  Consequently,
>>>> any subsequent kernel-mode access to the remapped address raises a fault.
>>>>
>>>> To fix it, define arch_mk_kernel_prot() to convert user prot to kernel
>>>> prot for arm64, and call arch_mk_kernel_prot() in generic_access_phys(),
>>>> so that a user prot is passed to ioremap_prot().
>>>>
>>>> Fixes: 893dea9ccd08 ("arm64: Add HAVE_IOREMAP_PROT support")
>>>> Signed-off-by: Zeng Heng <zengheng4 at huawei.com>
>>>> Signed-off-by: Jinjiang Tu <tujinjiang at huawei.com>
>>>> ---
>>>> Changes in v3:
>>>>    * arch_mk_kernel_prot() always grant read/write permissions.
>>>>
>>>>    arch/arm64/include/asm/io.h |  8 ++++++++
>>>>    mm/memory.c                 | 12 +++++++++++-
>>>>    2 files changed, 19 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
>>>> index 83e03abbb2ca..fe3040d59119 100644
>>>> --- a/arch/arm64/include/asm/io.h
>>>> +++ b/arch/arm64/include/asm/io.h
>>>> @@ -267,6 +267,14 @@ int arm64_ioremap_prot_hook_register(const ioremap_prot_hook_t hook);
>>>>    #define ioremap_prot ioremap_prot
>>>> +#define arch_mk_kernel_prot arch_mk_kernel_prot
>>>> +static inline pgprot_t arch_mk_kernel_prot(pgprot_t user_prot)
>>>> +{
>>>> +	ptdesc_t mem_type = pgprot_val(user_prot) & PTE_ATTRINDX_MASK;
>>>> +
>>>> +	return __pgprot_modify(PAGE_KERNEL, PTE_ATTRINDX_MASK, mem_type);
>>>> +}
>>> Do we really need another arch helper here?
>> For arc, powerpc, ioremap_prot() simply copy the user pte prot to the kernel page table too.
>> So maybe we should fix for the two archs too, and we should define a arch helper here.
>> But I'm not familiar with them.
> My point is that we already have the helper: ioremap_prot(). Just fix
> that for arm64 and cc the other arch maintainers if you're not sure how
> to fix it for them. What we don't need to do is add an additional helper.
>
ioremap_prot() may be called outside of arch/arm64 in the future, and I think
most of the cases will not pass a user prot to ioremap_prot().

generic_access_phys() is a special case, so I want to limit the modification to
generic_access_phys() only.

Thanks.

> Will
>