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linux-mm@kvack.org Subject: Re: [PATCH v3] arm64: mm: fix pass user prot to ioremap_prot in generic_access_phys Message-ID: References: <20260130073807.99474-1-tujinjiang@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260130073807.99474-1-tujinjiang@huawei.com> X-Rspamd-Server: rspam11 X-Stat-Signature: b5qjgjczh58exxunh8icyyaqfgbtrx5b X-Rspam-User: X-Rspamd-Queue-Id: A2AD0140004 X-HE-Tag: 1770044164-197114 X-HE-Meta: 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HvJCal8Bpl6gb2e3Lxv72HXtwFliZ0y3M0uSsUs5C3o5DEnK6Lwu+lRegZlwj2R/OoIXxhJqdnl/2MNR3uJgqDboVht+7OFXIqqzVQjU92CgRkf1L6q6QxKrYcku/92ySoaAFQztwh9dajoUahkllQG+UapayGe4CIq7c1k8UWNTw9ZzQyIN5UHCsd3D5PWdH9AcS1ppIPdoEH8zPrb7GvQiWrlzgMCoP2UZrrHOCrMpk0tPCVBzBKYmA3mxQJgKatAko71nltnlhBJsR3YydwqWmzhUFfxoOBAmkzKODAzHVb/efDj43w0wQwbaH142tALsP X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 > Signed-off-by: Jinjiang Tu > --- > 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? It looks to me like generic_access_phys() is the only caller of ioremap_prot() outside of arch/, so why not just handle the user_prot in there on arm64? You could rename the existing ioremap_prot() function in arch/arm64/mm/ioremap.c to e.g. __ioremap_prot(), switch over the callers in arch/arm64 and then add ioremap_prot() to wrap that with your pgprot modification above. Will