[PATCH 1/2] firmware_loader: annotate doctests as `no_run`

[PATCH 1/2] firmware_loader: annotate doctests as `no_run`

[Danilo Krummrich]

The doctests of `Firmware` are compile-time only tests, since they
require a proper `Device` and a valid path to a (firmware) blob in order
to do something sane on runtime - we can't satisfy both of those
requirements.

Hence, configure the example as `no_run`.

Unfortunately, the kernel's Rust build system can't consider the
`no_run` attribute yet. Hence, for the meantime, wrap the example code
into a new function and never actually call it.

Fixes: de6582833db0 ("rust: add firmware abstractions")
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
---
 rust/kernel/firmware.rs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
index 386c8fb44785..106a928a535e 100644
--- a/rust/kernel/firmware.rs
+++ b/rust/kernel/firmware.rs
@@ -26,14 +26,18 @@
 ///
 /// # Examples
 ///
-/// ```
+/// ```no_run
 /// # use kernel::{c_str, device::Device, firmware::Firmware};
 ///
+/// # fn no_run() -> Result<(), Error> {
 /// # // SAFETY: *NOT* safe, just for the example to get an `ARef<Device>` instance
 /// # let dev = unsafe { Device::from_raw(core::ptr::null_mut()) };
 ///
-/// let fw = Firmware::request(c_str!("path/to/firmware.bin"), &dev).unwrap();
+/// let fw = Firmware::request(c_str!("path/to/firmware.bin"), &dev)?;
 /// let blob = fw.data();
+///
+/// # Ok(())
+/// # }
 /// ```
 pub struct Firmware(NonNull<bindings::firmware>);
 

base-commit: 997197b58bf6e22b8c6ef88a168d8292fa9acec9
-- 
2.45.2

[PATCH 2/2] firmware_loader: fix soundness issue in `request_internal`

[Danilo Krummrich]

`request_internal` must be called with one of the following function
pointers: request_firmware(), firmware_request_nowarn(),
firmware_request_platform() or request_firmware_direct().

The previous `FwFunc` alias did not guarantee this, which is unsound.

In order to fix this up, implement `FwFunc` as new type with a
corresponding type invariant and unsafe `new` function.

Reported-by: Gary Guo <gary@garyguo.net>
Closes: https://lore.kernel.org/lkml/20240620143611.7995e0bb@eugeo/
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
---
 rust/kernel/firmware.rs | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
index 106a928a535e..d765ecc85d38 100644
--- a/rust/kernel/firmware.rs
+++ b/rust/kernel/firmware.rs
@@ -7,11 +7,24 @@
 use crate::{bindings, device::Device, error::Error, error::Result, str::CStr};
 use core::ptr::NonNull;
 
-// One of the following: `bindings::request_firmware`, `bindings::firmware_request_nowarn`,
-// `firmware_request_platform`, `bindings::request_firmware_direct`
-type FwFunc =
+type RawFwFunc =
     unsafe extern "C" fn(*mut *const bindings::firmware, *const i8, *mut bindings::device) -> i32;
 
+/// # Invariants
+///
+/// One of the following: `bindings::request_firmware`, `bindings::firmware_request_nowarn`,
+/// `firmware_request_platform`, `bindings::request_firmware_direct`
+struct FwFunc(RawFwFunc);
+
+impl FwFunc {
+    /// # Safety
+    ///
+    /// Must be one of the functions listed in the type invariants.
+    unsafe fn from_raw(func: RawFwFunc) -> Self {
+        Self(func)
+    }
+}
+
 /// Abstraction around a C `struct firmware`.
 ///
 /// This is a simple abstraction around the C firmware API. Just like with the C API, firmware can
@@ -48,7 +61,7 @@ fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
 
         // SAFETY: `pfw` is a valid pointer to a NULL initialized `bindings::firmware` pointer.
         // `name` and `dev` are valid as by their type invariants.
-        let ret = unsafe { func(pfw as _, name.as_char_ptr(), dev.as_raw()) };
+        let ret = unsafe { func.0(pfw as _, name.as_char_ptr(), dev.as_raw()) };
         if ret != 0 {
             return Err(Error::from_errno(ret));
         }
@@ -60,13 +73,20 @@ fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
 
     /// Send a firmware request and wait for it. See also `bindings::request_firmware`.
     pub fn request(name: &CStr, dev: &Device) -> Result<Self> {
-        Self::request_internal(name, dev, bindings::request_firmware)
+        // SAFETY: `bindings::request_firmware` is valid by the safety requirement of `FwFunc`.
+        let func = unsafe { FwFunc::from_raw(bindings::request_firmware) };
+
+        Self::request_internal(name, dev, func)
     }
 
     /// Send a request for an optional firmware module. See also
     /// `bindings::firmware_request_nowarn`.
     pub fn request_nowarn(name: &CStr, dev: &Device) -> Result<Self> {
-        Self::request_internal(name, dev, bindings::firmware_request_nowarn)
+        // SAFETY: `bindings::firmware_request_nowarn` is valid by the safety requirement of
+        // `FwFunc::new`.
+        let func = unsafe { FwFunc::from_raw(bindings::firmware_request_nowarn) };
+
+        Self::request_internal(name, dev, func)
     }
 
     fn as_raw(&self) -> *mut bindings::firmware {
-- 
2.45.2

Re: [PATCH 2/2] firmware_loader: fix soundness issue in `request_internal`

[Christian Schrefl]

Greetings.

On 07.07.24 2:38 AM, Danilo Krummrich wrote:
> `request_internal` must be called with one of the following function
> pointers: request_firmware(), firmware_request_nowarn(),
> firmware_request_platform() or request_firmware_direct().
> 
> The previous `FwFunc` alias did not guarantee this, which is unsound.
> 
> In order to fix this up, implement `FwFunc` as new type with a
> corresponding type invariant and unsafe `new` function.
> 
> Reported-by: Gary Guo <gary@garyguo.net>
> Closes: https://lore.kernel.org/lkml/20240620143611.7995e0bb@eugeo/
> Signed-off-by: Danilo Krummrich <dakr@redhat.com>
> ---
>  rust/kernel/firmware.rs | 32 ++++++++++++++++++++++++++------
>  1 file changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
> index 106a928a535e..d765ecc85d38 100644
> --- a/rust/kernel/firmware.rs
> +++ b/rust/kernel/firmware.rs
> @@ -7,11 +7,24 @@
>  use crate::{bindings, device::Device, error::Error, error::Result, str::CStr};
>  use core::ptr::NonNull;
>  
> -// One of the following: `bindings::request_firmware`, `bindings::firmware_request_nowarn`,
> -// `firmware_request_platform`, `bindings::request_firmware_direct`
> -type FwFunc =
> +type RawFwFunc =
>      unsafe extern "C" fn(*mut *const bindings::firmware, *const i8, *mut bindings::device) -> i32;
>  
> +/// # Invariants
> +///
> +/// One of the following: `bindings::request_firmware`, `bindings::firmware_request_nowarn`,
> +/// `firmware_request_platform`, `bindings::request_firmware_direct`
> +struct FwFunc(RawFwFunc);
> +
> +impl FwFunc {
> +    /// # Safety
> +    ///
> +    /// Must be one of the functions listed in the type invariants.
> +    unsafe fn from_raw(func: RawFwFunc) -> Self {
> +        Self(func)
> +    }
Why not write methods that construct each possible FwFunc?
That way the code that needs to know abut this invariant is only inside a single impl block.
Something like:
impl FwFunc {
    fn request_firmware() -> Self {
        // # Safety
        // As per the Type Invariant `bindings::request_firmware` is a valid vaule.
    	FwFunc(bindings::request_firmware)
    }
}

> +}
> +
>  /// Abstraction around a C `struct firmware`.
>  ///
>  /// This is a simple abstraction around the C firmware API. Just like with the C API, firmware can
> @@ -48,7 +61,7 @@ fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
>  
>          // SAFETY: `pfw` is a valid pointer to a NULL initialized `bindings::firmware` pointer.
>          // `name` and `dev` are valid as by their type invariants.
> -        let ret = unsafe { func(pfw as _, name.as_char_ptr(), dev.as_raw()) };
> +        let ret = unsafe { func.0(pfw as _, name.as_char_ptr(), dev.as_raw()) };
>          if ret != 0 {
>              return Err(Error::from_errno(ret));
>          }
> @@ -60,13 +73,20 @@ fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
>  
>      /// Send a firmware request and wait for it. See also `bindings::request_firmware`.
>      pub fn request(name: &CStr, dev: &Device) -> Result<Self> {
> -        Self::request_internal(name, dev, bindings::request_firmware)
> +        // SAFETY: `bindings::request_firmware` is valid by the safety requirement of `FwFunc`.
> +        let func = unsafe { FwFunc::from_raw(bindings::request_firmware) };
> +
> +        Self::request_internal(name, dev, func)
>      }
>  
>      /// Send a request for an optional firmware module. See also
>      /// `bindings::firmware_request_nowarn`.
>      pub fn request_nowarn(name: &CStr, dev: &Device) -> Result<Self> {
> -        Self::request_internal(name, dev, bindings::firmware_request_nowarn)
> +        // SAFETY: `bindings::firmware_request_nowarn` is valid by the safety requirement of
> +        // `FwFunc::new`.
> +        let func = unsafe { FwFunc::from_raw(bindings::firmware_request_nowarn) };
> +
> +        Self::request_internal(name, dev, func)
>      }
>  
>      fn as_raw(&self) -> *mut bindings::firmware {

Cheers,
Christian

Re: [PATCH 2/2] firmware_loader: fix soundness issue in `request_internal`

[Danilo Krummrich]

On Sun, Jul 07, 2024 at 10:57:31PM +0200, Christian Schrefl wrote:
> Greetings.
> 
> On 07.07.24 2:38 AM, Danilo Krummrich wrote:
> > `request_internal` must be called with one of the following function
> > pointers: request_firmware(), firmware_request_nowarn(),
> > firmware_request_platform() or request_firmware_direct().
> > 
> > The previous `FwFunc` alias did not guarantee this, which is unsound.
> > 
> > In order to fix this up, implement `FwFunc` as new type with a
> > corresponding type invariant and unsafe `new` function.
> > 
> > Reported-by: Gary Guo <gary@garyguo.net>
> > Closes: https://lore.kernel.org/lkml/20240620143611.7995e0bb@eugeo/
> > Signed-off-by: Danilo Krummrich <dakr@redhat.com>
> > ---
> >  rust/kernel/firmware.rs | 32 ++++++++++++++++++++++++++------
> >  1 file changed, 26 insertions(+), 6 deletions(-)
> > 
> > diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
> > index 106a928a535e..d765ecc85d38 100644
> > --- a/rust/kernel/firmware.rs
> > +++ b/rust/kernel/firmware.rs
> > @@ -7,11 +7,24 @@
> >  use crate::{bindings, device::Device, error::Error, error::Result, str::CStr};
> >  use core::ptr::NonNull;
> >  
> > -// One of the following: `bindings::request_firmware`, `bindings::firmware_request_nowarn`,
> > -// `firmware_request_platform`, `bindings::request_firmware_direct`
> > -type FwFunc =
> > +type RawFwFunc =
> >      unsafe extern "C" fn(*mut *const bindings::firmware, *const i8, *mut bindings::device) -> i32;
> >  
> > +/// # Invariants
> > +///
> > +/// One of the following: `bindings::request_firmware`, `bindings::firmware_request_nowarn`,
> > +/// `firmware_request_platform`, `bindings::request_firmware_direct`
> > +struct FwFunc(RawFwFunc);
> > +
> > +impl FwFunc {
> > +    /// # Safety
> > +    ///
> > +    /// Must be one of the functions listed in the type invariants.
> > +    unsafe fn from_raw(func: RawFwFunc) -> Self {
> > +        Self(func)
> > +    }
> Why not write methods that construct each possible FwFunc?

Thanks, this is a good idea indeed, will send a v2.

> That way the code that needs to know abut this invariant is only inside a single impl block.
> Something like:
> impl FwFunc {
>     fn request_firmware() -> Self {
>         // # Safety
>         // As per the Type Invariant `bindings::request_firmware` is a valid vaule.
>     	FwFunc(bindings::request_firmware)
>     }
> }
> 
> > +}
> > +
> >  /// Abstraction around a C `struct firmware`.
> >  ///
> >  /// This is a simple abstraction around the C firmware API. Just like with the C API, firmware can
> > @@ -48,7 +61,7 @@ fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
> >  
> >          // SAFETY: `pfw` is a valid pointer to a NULL initialized `bindings::firmware` pointer.
> >          // `name` and `dev` are valid as by their type invariants.
> > -        let ret = unsafe { func(pfw as _, name.as_char_ptr(), dev.as_raw()) };
> > +        let ret = unsafe { func.0(pfw as _, name.as_char_ptr(), dev.as_raw()) };
> >          if ret != 0 {
> >              return Err(Error::from_errno(ret));
> >          }
> > @@ -60,13 +73,20 @@ fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
> >  
> >      /// Send a firmware request and wait for it. See also `bindings::request_firmware`.
> >      pub fn request(name: &CStr, dev: &Device) -> Result<Self> {
> > -        Self::request_internal(name, dev, bindings::request_firmware)
> > +        // SAFETY: `bindings::request_firmware` is valid by the safety requirement of `FwFunc`.
> > +        let func = unsafe { FwFunc::from_raw(bindings::request_firmware) };
> > +
> > +        Self::request_internal(name, dev, func)
> >      }
> >  
> >      /// Send a request for an optional firmware module. See also
> >      /// `bindings::firmware_request_nowarn`.
> >      pub fn request_nowarn(name: &CStr, dev: &Device) -> Result<Self> {
> > -        Self::request_internal(name, dev, bindings::firmware_request_nowarn)
> > +        // SAFETY: `bindings::firmware_request_nowarn` is valid by the safety requirement of
> > +        // `FwFunc::new`.
> > +        let func = unsafe { FwFunc::from_raw(bindings::firmware_request_nowarn) };
> > +
> > +        Self::request_internal(name, dev, func)
> >      }
> >  
> >      fn as_raw(&self) -> *mut bindings::firmware {
> 
> Cheers,
> Christian
>