ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 75 insertions, 0 deletions

diff --git a/rust/syn/export.rs b/rust/syn/export.rs
new file mode 100644
index 000000000..05dad324b
--- /dev/null
+++ b/rust/syn/export.rs
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+#[doc(hidden)]
+pub use std::clone::Clone;
+#[doc(hidden)]
+pub use std::cmp::{Eq, PartialEq};
+#[doc(hidden)]
+pub use std::concat;
+#[doc(hidden)]
+pub use std::default::Default;
+#[doc(hidden)]
+pub use std::fmt::Debug;
+#[doc(hidden)]
+pub use std::hash::{Hash, Hasher};
+#[doc(hidden)]
+pub use std::marker::Copy;
+#[doc(hidden)]
+pub use std::option::Option::{None, Some};
+#[doc(hidden)]
+pub use std::result::Result::{Err, Ok};
+#[doc(hidden)]
+pub use std::stringify;
+
+#[doc(hidden)]
+pub type Formatter<'a> = std::fmt::Formatter<'a>;
+#[doc(hidden)]
+pub type FmtResult = std::fmt::Result;
+
+#[doc(hidden)]
+pub type bool = std::primitive::bool;
+#[doc(hidden)]
+pub type str = std::primitive::str;
+
+#[cfg(feature = "printing")]
+#[doc(hidden)]
+pub use quote;
+
+#[doc(hidden)]
+pub type Span = proc_macro2::Span;
+#[doc(hidden)]
+pub type TokenStream2 = proc_macro2::TokenStream;
+
+#[cfg(feature = "parsing")]
+#[doc(hidden)]
+pub use crate::group::{parse_braces, parse_brackets, parse_parens};
+
+#[doc(hidden)]
+pub use crate::span::IntoSpans;
+
+#[cfg(all(feature = "parsing", feature = "printing"))]
+#[doc(hidden)]
+pub use crate::parse_quote::parse as parse_quote;
+
+#[cfg(feature = "parsing")]
+#[doc(hidden)]
+pub use crate::token::parsing::{peek_punct, punct as parse_punct};
+
+#[cfg(feature = "printing")]
+#[doc(hidden)]
+pub use crate::token::printing::punct as print_punct;
+
+#[cfg(feature = "parsing")]
+#[doc(hidden)]
+pub use crate::token::private::CustomToken;
+
+#[cfg(feature = "proc-macro")]
+#[doc(hidden)]
+pub type TokenStream = proc_macro::TokenStream;
+
+#[cfg(feature = "printing")]
+#[doc(hidden)]
+pub use quote::{ToTokens, TokenStreamExt};
+
+#[doc(hidden)]
+pub struct private(pub(crate) ());