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, 158 insertions, 0 deletions

diff --git a/rust/syn/lifetime.rs b/rust/syn/lifetime.rs
new file mode 100644
index 000000000..24bec7fe9
--- /dev/null
+++ b/rust/syn/lifetime.rs
@@ -0,0 +1,158 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+#[cfg(feature = "parsing")]
+use crate::lookahead;
+use proc_macro2::{Ident, Span};
+use std::cmp::Ordering;
+use std::fmt::{self, Display};
+use std::hash::{Hash, Hasher};
+
+/// A Rust lifetime: `'a`.
+///
+/// Lifetime names must conform to the following rules:
+///
+/// - Must start with an apostrophe.
+/// - Must not consist of just an apostrophe: `'`.
+/// - Character after the apostrophe must be `_` or a Unicode code point with
+///   the XID_Start property.
+/// - All following characters must be Unicode code points with the XID_Continue
+///   property.
+pub struct Lifetime {
+    pub apostrophe: Span,
+    pub ident: Ident,
+}
+
+impl Lifetime {
+    /// # Panics
+    ///
+    /// Panics if the lifetime does not conform to the bulleted rules above.
+    ///
+    /// # Invocation
+    ///
+    /// ```
+    /// # use proc_macro2::Span;
+    /// # use syn::Lifetime;
+    /// #
+    /// # fn f() -> Lifetime {
+    /// Lifetime::new("'a", Span::call_site())
+    /// # }
+    /// ```
+    pub fn new(symbol: &str, span: Span) -> Self {
+        if !symbol.starts_with('\'') {
+            panic!(
+                "lifetime name must start with apostrophe as in \"'a\", got {:?}",
+                symbol
+            );
+        }
+
+        if symbol == "'" {
+            panic!("lifetime name must not be empty");
+        }
+
+        if !crate::ident::xid_ok(&symbol[1..]) {
+            panic!("{:?} is not a valid lifetime name", symbol);
+        }
+
+        Lifetime {
+            apostrophe: span,
+            ident: Ident::new(&symbol[1..], span),
+        }
+    }
+
+    pub fn span(&self) -> Span {
+        self.apostrophe
+            .join(self.ident.span())
+            .unwrap_or(self.apostrophe)
+    }
+
+    pub fn set_span(&mut self, span: Span) {
+        self.apostrophe = span;
+        self.ident.set_span(span);
+    }
+}
+
+impl Display for Lifetime {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        "'".fmt(formatter)?;
+        self.ident.fmt(formatter)
+    }
+}
+
+impl Clone for Lifetime {
+    fn clone(&self) -> Self {
+        Lifetime {
+            apostrophe: self.apostrophe,
+            ident: self.ident.clone(),
+        }
+    }
+}
+
+impl PartialEq for Lifetime {
+    fn eq(&self, other: &Lifetime) -> bool {
+        self.ident.eq(&other.ident)
+    }
+}
+
+impl Eq for Lifetime {}
+
+impl PartialOrd for Lifetime {
+    fn partial_cmp(&self, other: &Lifetime) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Lifetime {
+    fn cmp(&self, other: &Lifetime) -> Ordering {
+        self.ident.cmp(&other.ident)
+    }
+}
+
+impl Hash for Lifetime {
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        self.ident.hash(h);
+    }
+}
+
+#[cfg(feature = "parsing")]
+pub_if_not_doc! {
+    #[doc(hidden)]
+    #[allow(non_snake_case)]
+    pub fn Lifetime(marker: lookahead::TokenMarker) -> Lifetime {
+        match marker {}
+    }
+}
+
+#[cfg(feature = "parsing")]
+pub(crate) mod parsing {
+    use crate::error::Result;
+    use crate::lifetime::Lifetime;
+    use crate::parse::{Parse, ParseStream};
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for Lifetime {
+        fn parse(input: ParseStream) -> Result<Self> {
+            input.step(|cursor| {
+                cursor
+                    .lifetime()
+                    .ok_or_else(|| cursor.error("expected lifetime"))
+            })
+        }
+    }
+}
+
+#[cfg(feature = "printing")]
+mod printing {
+    use crate::lifetime::Lifetime;
+    use proc_macro2::{Punct, Spacing, TokenStream};
+    use quote::{ToTokens, TokenStreamExt};
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
+    impl ToTokens for Lifetime {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            let mut apostrophe = Punct::new('\'', Spacing::Joint);
+            apostrophe.set_span(self.apostrophe);
+            tokens.append(apostrophe);
+            self.ident.to_tokens(tokens);
+        }
+    }
+}