From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions 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) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- samples/rust/rust_configfs.rs | 191 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 191 insertions(+) create mode 100644 samples/rust/rust_configfs.rs (limited to 'samples/rust/rust_configfs.rs') diff --git a/samples/rust/rust_configfs.rs b/samples/rust/rust_configfs.rs new file mode 100644 index 000000000..a1bd9db60 --- /dev/null +++ b/samples/rust/rust_configfs.rs @@ -0,0 +1,191 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Rust configfs sample. + +use kernel::alloc::flags; +use kernel::configfs; +use kernel::configfs::configfs_attrs; +use kernel::new_mutex; +use kernel::page::PAGE_SIZE; +use kernel::prelude::*; +use kernel::sync::Mutex; + +module! { + type: RustConfigfs, + name: "rust_configfs", + authors: ["Rust for Linux Contributors"], + description: "Rust configfs sample", + license: "GPL", +} + +#[pin_data] +struct RustConfigfs { + #[pin] + config: configfs::Subsystem, +} + +#[pin_data] +struct Configuration { + message: &'static CStr, + #[pin] + bar: Mutex<(KBox<[u8; PAGE_SIZE]>, usize)>, +} + +impl Configuration { + fn new() -> impl PinInit { + try_pin_init!(Self { + message: c"Hello World\n", + bar <- new_mutex!((KBox::new([0; PAGE_SIZE], flags::GFP_KERNEL)?, 0)), + }) + } +} + +impl kernel::InPlaceModule for RustConfigfs { + fn init(_module: &'static ThisModule) -> impl PinInit { + pr_info!("Rust configfs sample (init)\n"); + + // Define a subsystem with the data type `Configuration`, two + // attributes, `message` and `bar` and child group type `Child`. `mkdir` + // in the directory representing this subsystem will create directories + // backed by the `Child` type. + let item_type = configfs_attrs! { + container: configfs::Subsystem, + data: Configuration, + child: Child, + attributes: [ + message: 0, + bar: 1, + ], + }; + + try_pin_init!(Self { + config <- configfs::Subsystem::new( + c"rust_configfs", item_type, Configuration::new() + ), + }) + } +} + +#[vtable] +impl configfs::GroupOperations for Configuration { + type Child = Child; + + fn make_group(&self, name: &CStr) -> Result, Error>> { + // Define a group with data type `Child`, one attribute `baz` and child + // group type `GrandChild`. `mkdir` in the directory representing this + // group will create directories backed by the `GrandChild` type. + let tpe = configfs_attrs! { + container: configfs::Group, + data: Child, + child: GrandChild, + attributes: [ + baz: 0, + ], + }; + + Ok(configfs::Group::new(name.try_into()?, tpe, Child::new())) + } +} + +#[vtable] +impl configfs::AttributeOperations<0> for Configuration { + type Data = Configuration; + + fn show(container: &Configuration, page: &mut [u8; PAGE_SIZE]) -> Result { + pr_info!("Show message\n"); + let data = container.message.to_bytes(); + page[0..data.len()].copy_from_slice(data); + Ok(data.len()) + } +} + +#[vtable] +impl configfs::AttributeOperations<1> for Configuration { + type Data = Configuration; + + fn show(container: &Configuration, page: &mut [u8; PAGE_SIZE]) -> Result { + pr_info!("Show bar\n"); + let guard = container.bar.lock(); + let data = guard.0.as_slice(); + let len = guard.1; + page[0..len].copy_from_slice(&data[0..len]); + Ok(len) + } + + fn store(container: &Configuration, page: &[u8]) -> Result { + pr_info!("Store bar\n"); + let mut guard = container.bar.lock(); + guard.0[0..page.len()].copy_from_slice(page); + guard.1 = page.len(); + Ok(()) + } +} + +// `pin_data` cannot handle structs without braces. +#[pin_data] +struct Child {} + +impl Child { + fn new() -> impl PinInit { + try_pin_init!(Self {}) + } +} + +#[vtable] +impl configfs::GroupOperations for Child { + type Child = GrandChild; + + fn make_group(&self, name: &CStr) -> Result, Error>> { + // Define a group with data type `GrandChild`, one attribute `gc`. As no + // child type is specified, it will not be possible to create subgroups + // in this group, and `mkdir`in the directory representing this group + // will return an error. + let tpe = configfs_attrs! { + container: configfs::Group, + data: GrandChild, + attributes: [ + gc: 0, + ], + }; + + Ok(configfs::Group::new( + name.try_into()?, + tpe, + GrandChild::new(), + )) + } +} + +#[vtable] +impl configfs::AttributeOperations<0> for Child { + type Data = Child; + + fn show(_container: &Child, page: &mut [u8; PAGE_SIZE]) -> Result { + pr_info!("Show baz\n"); + let data = c"Hello Baz\n".to_bytes(); + page[0..data.len()].copy_from_slice(data); + Ok(data.len()) + } +} + +// `pin_data` cannot handle structs without braces. +#[pin_data] +struct GrandChild {} + +impl GrandChild { + fn new() -> impl PinInit { + try_pin_init!(Self {}) + } +} + +#[vtable] +impl configfs::AttributeOperations<0> for GrandChild { + type Data = GrandChild; + + fn show(_container: &GrandChild, page: &mut [u8; PAGE_SIZE]) -> Result { + pr_info!("Show grand child\n"); + let data = c"Hello GC\n".to_bytes(); + page[0..data.len()].copy_from_slice(data); + Ok(data.len()) + } +} -- cgit v1.3.1