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

6 files changed, 253 insertions, 0 deletions

diff --git a/drivers/gpu/drm/nova/Kconfig b/drivers/gpu/drm/nova/Kconfig
new file mode 100644
index 000000000..ba16c7440
--- /dev/null
+++ b/drivers/gpu/drm/nova/Kconfig
@@ -0,0 +1,17 @@
+config DRM_NOVA
+	tristate "Nova DRM driver"
+	depends on 64BIT
+	depends on DRM=y
+	depends on PCI
+	depends on RUST
+	depends on !CPU_BIG_ENDIAN
+	select AUXILIARY_BUS
+	select NOVA_CORE
+	default n
+	help
+	  Choose this if you want to build the Nova DRM driver for Nvidia
+	  GSP-based GPUs.
+
+	  This driver is work in progress and may not be functional.
+
+	  If M is selected, the module will be called nova-drm.
diff --git a/drivers/gpu/drm/nova/Makefile b/drivers/gpu/drm/nova/Makefile
new file mode 100644
index 000000000..6355f7502
--- /dev/null
+++ b/drivers/gpu/drm/nova/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+# nova-drm is built from drivers/gpu/Makefile.
+# nova.o (rust-analyzer marker - DO NOT REMOVE).
diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs
new file mode 100644
index 000000000..60752bccd
--- /dev/null
+++ b/drivers/gpu/drm/nova/driver.rs
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use kernel::{
+    auxiliary,
+    device::{
+        Core,
+        DeviceContext, //
+    },
+    drm::{
+        self,
+        gem,
+        ioctl, //
+    },
+    prelude::*,
+    sync::aref::ARef, //
+};
+
+use crate::file::File;
+use crate::gem::NovaObject;
+
+pub(crate) struct NovaDriver;
+
+pub(crate) struct Nova<'bound> {
+    #[expect(unused)]
+    drm: ARef<drm::Device<NovaDriver>>,
+    _reg: drm::Registration<'bound, NovaDriver>,
+}
+
+/// Convienence type alias for the DRM device type for this driver
+pub(crate) type NovaDevice<Ctx = drm::Normal> = drm::Device<NovaDriver, Ctx>;
+
+const INFO: drm::DriverInfo = drm::DriverInfo {
+    major: 0,
+    minor: 0,
+    patchlevel: 0,
+    name: c"nova-drm",
+    desc: c"NVIDIA Graphics and Compute",
+};
+
+const NOVA_CORE_MODULE_NAME: &CStr = c"nova-core";
+const AUXILIARY_NAME: &CStr = c"nova-drm";
+
+kernel::auxiliary_device_table!(
+    AUX_TABLE,
+    <NovaDriver as auxiliary::Driver>::IdInfo,
+    [(
+        auxiliary::DeviceId::new(NOVA_CORE_MODULE_NAME, AUXILIARY_NAME),
+        ()
+    )]
+);
+
+impl auxiliary::Driver for NovaDriver {
+    type IdInfo = ();
+    type Data<'bound> = Nova<'bound>;
+    const ID_TABLE: auxiliary::IdTable<Self::IdInfo> = &AUX_TABLE;
+
+    fn probe<'bound>(
+        adev: &'bound auxiliary::Device<Core<'_>>,
+        _info: &'bound Self::IdInfo,
+    ) -> impl PinInit<Self::Data<'bound>, Error> + 'bound {
+        let drm = drm::UnregisteredDevice::<Self>::new(adev, Ok(()))?;
+        // SAFETY: `reg` is stored in `Nova` and dropped when the driver is unbound; it is
+        // never forgotten.
+        let reg = unsafe { drm::Registration::new(adev.as_ref(), drm, (), 0)? };
+
+        Ok(Nova {
+            drm: reg.device().into(),
+            _reg: reg,
+        })
+    }
+}
+
+#[vtable]
+impl drm::Driver for NovaDriver {
+    type Data = ();
+    type RegistrationData<'a> = ();
+    type File = File;
+    type Object = gem::Object<NovaObject>;
+    type ParentDevice<Ctx: DeviceContext> = auxiliary::Device<Ctx>;
+
+    const INFO: drm::DriverInfo = INFO;
+
+    kernel::declare_drm_ioctls! {
+        (NOVA_GETPARAM, drm_nova_getparam, ioctl::RENDER_ALLOW, File::get_param),
+        (NOVA_GEM_CREATE, drm_nova_gem_create, ioctl::AUTH | ioctl::RENDER_ALLOW, File::gem_create),
+        (NOVA_GEM_INFO, drm_nova_gem_info, ioctl::AUTH | ioctl::RENDER_ALLOW, File::gem_info),
+    }
+}
diff --git a/drivers/gpu/drm/nova/file.rs b/drivers/gpu/drm/nova/file.rs
new file mode 100644
index 000000000..298c02bac
--- /dev/null
+++ b/drivers/gpu/drm/nova/file.rs
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use crate::driver::{NovaDevice, NovaDriver};
+use crate::gem::NovaObject;
+use kernel::{
+    alloc::flags::*,
+    auxiliary,
+    device::Bound,
+    drm::{
+        self,
+        gem::BaseObject,
+        Registered, //
+    },
+    pci,
+    prelude::*,
+    uapi,
+};
+
+pub(crate) struct File;
+
+impl drm::file::DriverFile for File {
+    type Driver = NovaDriver;
+
+    fn open(_dev: &NovaDevice) -> Result<Pin<KBox<Self>>> {
+        Ok(KBox::new(Self, GFP_KERNEL)?.into())
+    }
+}
+
+impl File {
+    /// IOCTL: get_param: Query GPU / driver metadata.
+    pub(crate) fn get_param(
+        dev: &NovaDevice<Registered>,
+        _reg_data: &(),
+        getparam: &mut uapi::drm_nova_getparam,
+        _file: &drm::File<File>,
+    ) -> Result<u32> {
+        let adev: &auxiliary::Device<Bound> = dev.as_ref();
+        let pdev: &pci::Device<Bound> = adev.parent().try_into()?;
+
+        let value = match getparam.param as u32 {
+            uapi::NOVA_GETPARAM_VRAM_BAR_SIZE => pdev.resource_len(1)?,
+            _ => return Err(EINVAL),
+        };
+
+        getparam.value = Into::<u64>::into(value);
+
+        Ok(0)
+    }
+
+    /// IOCTL: gem_create: Create a new DRM GEM object.
+    pub(crate) fn gem_create(
+        dev: &NovaDevice<Registered>,
+        _reg_data: &(),
+        req: &mut uapi::drm_nova_gem_create,
+        file: &drm::File<File>,
+    ) -> Result<u32> {
+        let obj = NovaObject::new(dev, req.size.try_into()?)?;
+
+        req.handle = obj.create_handle(file)?;
+
+        Ok(0)
+    }
+
+    /// IOCTL: gem_info: Query GEM metadata.
+    pub(crate) fn gem_info(
+        _dev: &NovaDevice<Registered>,
+        _reg_data: &(),
+        req: &mut uapi::drm_nova_gem_info,
+        file: &drm::File<File>,
+    ) -> Result<u32> {
+        let bo = NovaObject::lookup_handle(file, req.handle)?;
+
+        req.size = bo.size().try_into()?;
+
+        Ok(0)
+    }
+}
diff --git a/drivers/gpu/drm/nova/gem.rs b/drivers/gpu/drm/nova/gem.rs
new file mode 100644
index 000000000..2b6fe9dc0
--- /dev/null
+++ b/drivers/gpu/drm/nova/gem.rs
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use kernel::{
+    drm,
+    drm::{
+        gem,
+        gem::BaseObject, //
+    },
+    page,
+    prelude::*,
+    sync::aref::ARef,
+};
+
+use crate::{
+    driver::{NovaDevice, NovaDriver},
+    file::File,
+};
+
+/// GEM Object inner driver data
+#[pin_data]
+pub(crate) struct NovaObject {}
+
+impl gem::DriverObject for NovaObject {
+    type Driver = NovaDriver;
+    type Args = ();
+
+    fn new(_dev: &NovaDevice, _size: usize, _args: Self::Args) -> impl PinInit<Self, Error> {
+        try_pin_init!(NovaObject {})
+    }
+}
+
+impl NovaObject {
+    /// Create a new DRM GEM object.
+    pub(crate) fn new(dev: &NovaDevice, size: usize) -> Result<ARef<gem::Object<Self>>> {
+        if size == 0 {
+            return Err(EINVAL);
+        }
+        let aligned_size = page::page_align(size).ok_or(EINVAL)?;
+
+        gem::Object::<Self>::new(dev, aligned_size, ())
+    }
+
+    /// Look up a GEM object handle for a `File` and return an `ObjectRef` for it.
+    #[inline]
+    pub(crate) fn lookup_handle(
+        file: &drm::File<File>,
+        handle: u32,
+    ) -> Result<ARef<gem::Object<Self>>> {
+        gem::Object::lookup_handle(file, handle)
+    }
+}
diff --git a/drivers/gpu/drm/nova/nova.rs b/drivers/gpu/drm/nova/nova.rs
new file mode 100644
index 000000000..1fd454c7e
--- /dev/null
+++ b/drivers/gpu/drm/nova/nova.rs
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Nova DRM Driver
+
+mod driver;
+mod file;
+mod gem;
+
+use crate::driver::NovaDriver;
+
+kernel::module_auxiliary_driver! {
+    type: NovaDriver,
+    name: "nova-drm",
+    authors: ["Danilo Krummrich"],
+    description: "Nova GPU driver",
+    license: "GPL v2",
+}