x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 227 insertions, 0 deletions

diff --git a/rust/syn/mac.rs b/rust/syn/mac.rs
new file mode 100644
index 000000000..ce4b022b4
--- /dev/null
+++ b/rust/syn/mac.rs
@@ -0,0 +1,227 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+#[cfg(feature = "parsing")]
+use crate::error::Result;
+#[cfg(feature = "parsing")]
+use crate::parse::{Parse, ParseStream, Parser};
+use crate::path::Path;
+use crate::token::{Brace, Bracket, Paren};
+use proc_macro2::extra::DelimSpan;
+#[cfg(feature = "parsing")]
+use proc_macro2::Delimiter;
+use proc_macro2::TokenStream;
+#[cfg(feature = "parsing")]
+use proc_macro2::TokenTree;
+
+ast_struct! {
+    /// A macro invocation: `println!("{}", mac)`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct Macro {
+        pub path: Path,
+        pub bang_token: Token![!],
+        pub delimiter: MacroDelimiter,
+        pub tokens: TokenStream,
+    }
+}
+
+ast_enum! {
+    /// A grouping token that surrounds a macro body: `m!(...)` or `m!{...}` or `m![...]`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub enum MacroDelimiter {
+        Paren(Paren),
+        Brace(Brace),
+        Bracket(Bracket),
+    }
+}
+
+impl MacroDelimiter {
+    pub fn span(&self) -> &DelimSpan {
+        match self {
+            MacroDelimiter::Paren(token) => &token.span,
+            MacroDelimiter::Brace(token) => &token.span,
+            MacroDelimiter::Bracket(token) => &token.span,
+        }
+    }
+
+    #[cfg(all(feature = "full", any(feature = "parsing", feature = "printing")))]
+    pub(crate) fn is_brace(&self) -> bool {
+        match self {
+            MacroDelimiter::Brace(_) => true,
+            MacroDelimiter::Paren(_) | MacroDelimiter::Bracket(_) => false,
+        }
+    }
+}
+
+impl Macro {
+    /// Parse the tokens within the macro invocation's delimiters into a syntax
+    /// tree.
+    ///
+    /// This is equivalent to `syn::parse2::<T>(mac.tokens)` except that it
+    /// produces a more useful span when `tokens` is empty.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use syn::{parse_quote, Expr, ExprLit, Ident, Lit, LitStr, Macro, Token};
+    /// use syn::ext::IdentExt;
+    /// use syn::parse::{Error, Parse, ParseStream, Result};
+    /// use syn::punctuated::Punctuated;
+    ///
+    /// // The arguments expected by libcore's format_args macro, and as a
+    /// // result most other formatting and printing macros like println.
+    /// //
+    /// //     println!("{} is {number:.prec$}", "x", prec=5, number=0.01)
+    /// struct FormatArgs {
+    ///     format_string: Expr,
+    ///     positional_args: Vec<Expr>,
+    ///     named_args: Vec<(Ident, Expr)>,
+    /// }
+    ///
+    /// impl Parse for FormatArgs {
+    ///     fn parse(input: ParseStream) -> Result<Self> {
+    ///         let format_string: Expr;
+    ///         let mut positional_args = Vec::new();
+    ///         let mut named_args = Vec::new();
+    ///
+    ///         format_string = input.parse()?;
+    ///         while !input.is_empty() {
+    ///             input.parse::<Token![,]>()?;
+    ///             if input.is_empty() {
+    ///                 break;
+    ///             }
+    ///             if input.peek(Ident::peek_any) && input.peek2(Token![=]) {
+    ///                 while !input.is_empty() {
+    ///                     let name: Ident = input.call(Ident::parse_any)?;
+    ///                     input.parse::<Token![=]>()?;
+    ///                     let value: Expr = input.parse()?;
+    ///                     named_args.push((name, value));
+    ///                     if input.is_empty() {
+    ///                         break;
+    ///                     }
+    ///                     input.parse::<Token![,]>()?;
+    ///                 }
+    ///                 break;
+    ///             }
+    ///             positional_args.push(input.parse()?);
+    ///         }
+    ///
+    ///         Ok(FormatArgs {
+    ///             format_string,
+    ///             positional_args,
+    ///             named_args,
+    ///         })
+    ///     }
+    /// }
+    ///
+    /// // Extract the first argument, the format string literal, from an
+    /// // invocation of a formatting or printing macro.
+    /// fn get_format_string(m: &Macro) -> Result<LitStr> {
+    ///     let args: FormatArgs = m.parse_body()?;
+    ///     match args.format_string {
+    ///         Expr::Lit(ExprLit { lit: Lit::Str(lit), .. }) => Ok(lit),
+    ///         other => {
+    ///             // First argument was not a string literal expression.
+    ///             // Maybe something like: println!(concat!(...), ...)
+    ///             Err(Error::new_spanned(other, "format string must be a string literal"))
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// fn main() {
+    ///     let invocation = parse_quote! {
+    ///         println!("{:?}", Instant::now())
+    ///     };
+    ///     let lit = get_format_string(&invocation).unwrap();
+    ///     assert_eq!(lit.value(), "{:?}");
+    /// }
+    /// ```
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    pub fn parse_body<T: Parse>(&self) -> Result<T> {
+        self.parse_body_with(T::parse)
+    }
+
+    /// Parse the tokens within the macro invocation's delimiters using the
+    /// given parser.
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    pub fn parse_body_with<F: Parser>(&self, parser: F) -> Result<F::Output> {
+        let scope = self.delimiter.span().close();
+        crate::parse::parse_scoped(parser, scope, self.tokens.clone())
+    }
+}
+
+#[cfg(feature = "parsing")]
+pub(crate) fn parse_delimiter(input: ParseStream) -> Result<(MacroDelimiter, TokenStream)> {
+    input.step(|cursor| {
+        if let Some((TokenTree::Group(g), rest)) = cursor.token_tree() {
+            let span = g.delim_span();
+            let delimiter = match g.delimiter() {
+                Delimiter::Parenthesis => MacroDelimiter::Paren(Paren(span)),
+                Delimiter::Brace => MacroDelimiter::Brace(Brace(span)),
+                Delimiter::Bracket => MacroDelimiter::Bracket(Bracket(span)),
+                Delimiter::None => {
+                    return Err(cursor.error("expected delimiter"));
+                }
+            };
+            Ok(((delimiter, g.stream()), rest))
+        } else {
+            Err(cursor.error("expected delimiter"))
+        }
+    })
+}
+
+#[cfg(feature = "parsing")]
+pub(crate) mod parsing {
+    use crate::error::Result;
+    use crate::mac::{parse_delimiter, Macro};
+    use crate::parse::{Parse, ParseStream};
+    use crate::path::Path;
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for Macro {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let tokens;
+            Ok(Macro {
+                path: input.call(Path::parse_mod_style)?,
+                bang_token: input.parse()?,
+                delimiter: {
+                    let (delimiter, content) = parse_delimiter(input)?;
+                    tokens = content;
+                    delimiter
+                },
+                tokens,
+            })
+        }
+    }
+}
+
+#[cfg(feature = "printing")]
+mod printing {
+    use crate::mac::{Macro, MacroDelimiter};
+    use crate::path;
+    use crate::path::printing::PathStyle;
+    use crate::token;
+    use proc_macro2::{Delimiter, TokenStream};
+    use quote::ToTokens;
+
+    impl MacroDelimiter {
+        pub(crate) fn surround(&self, tokens: &mut TokenStream, inner: TokenStream) {
+            let (delim, span) = match self {
+                MacroDelimiter::Paren(paren) => (Delimiter::Parenthesis, paren.span),
+                MacroDelimiter::Brace(brace) => (Delimiter::Brace, brace.span),
+                MacroDelimiter::Bracket(bracket) => (Delimiter::Bracket, bracket.span),
+            };
+            token::printing::delim(delim, span.join(), tokens, inner);
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
+    impl ToTokens for Macro {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            path::printing::print_path(tokens, &self.path, PathStyle::Mod);
+            self.bang_token.to_tokens(tokens);
+            self.delimiter.surround(tokens, self.tokens.clone());
+        }
+    }
+}