[PATCH v2] arm64: mm: fix pass user prot to ioremap_prot in generic_access_phys
Jinjiang Tu
tujinjiang at huawei.com
Tue Jan 27 23:12:56 PST 2026
在 2026/1/27 17:01, Jinjiang Tu 写道:
> 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>
> ---
> Change since v1:
> * fix in ther caller generic_access_phys(), suggested by Catalin Marinas.
>
> arch/arm64/include/asm/io.h | 11 +++++++++++
> mm/memory.c | 12 +++++++++++-
> 2 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
> index 83e03abbb2ca..fe8607eafab6 100644
> --- a/arch/arm64/include/asm/io.h
> +++ b/arch/arm64/include/asm/io.h
> @@ -267,6 +267,17 @@ 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)
> +{
> + unsigned long kernel_prot_val;
> +
> + kernel_prot_val = _PAGE_KERNEL & ~(PTE_WRITE | PTE_ATTRINDX_MASK);
> + kernel_prot_val |= pgprot_val(user_prot) & (PTE_WRITE | PTE_ATTRINDX_MASK);
> +
> + return __pgprot(kernel_prot_val);
> +}
I found I misunderstand the READ/WRITE permisson here.
If the pte is writeale, the PTE_WRITE is 1, and PTE_RDONLY means dirty or not (With DBM).
If the pte is read-only, the PTE_WRITE is 0, and PTE_RDONLY is 1.
Since generic_access_phys() have checked if the user can write with:
if ((write & FOLL_WRITE) && !pte_write(pte))
return -EINVAL;
So, maybe we could always grant writable permission, just as x86's ioremap() does?
Thanks.
> +
> #define _PAGE_IOREMAP PROT_DEVICE_nGnRE
>
> #define ioremap_wc(addr, size) \
> diff --git a/mm/memory.c b/mm/memory.c
> index da360a6eb8a4..68fcfc3bbad8 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -6836,6 +6836,14 @@ void follow_pfnmap_end(struct follow_pfnmap_args *args)
> EXPORT_SYMBOL_GPL(follow_pfnmap_end);
>
> #ifdef CONFIG_HAVE_IOREMAP_PROT
> +#ifndef arch_mk_kernel_prot
> +#define arch_mk_kernel_prot arch_mk_kernel_prot
> +static inline pgprot_t arch_mk_kernel_prot(pgprot_t user_prot)
> +{
> + return user_prot;
> +}
> +#endif
> +
> /**
> * generic_access_phys - generic implementation for iomem mmap access
> * @vma: the vma to access
> @@ -6853,6 +6861,7 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
> {
> resource_size_t phys_addr;
> pgprot_t prot = __pgprot(0);
> + pgprot_t kernel_prot;
> void __iomem *maddr;
> int offset = offset_in_page(addr);
> int ret = -EINVAL;
> @@ -6870,7 +6879,8 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
> if ((write & FOLL_WRITE) && !writable)
> return -EINVAL;
>
> - maddr = ioremap_prot(phys_addr, PAGE_ALIGN(len + offset), prot);
> + kernel_prot = arch_mk_kernel_prot(prot);
> + maddr = ioremap_prot(phys_addr, PAGE_ALIGN(len + offset), kernel_prot);
> if (!maddr)
> return -ENOMEM;
>
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