Re: [PATCH RFT v12 4/8] fork: Add shadow stack support to clone3()

[Yury Khrustalev <yury.khrustalev@arm.com>]

On Thu, Oct 31, 2024 at 07:25:05PM +0000, Mark Brown wrote:
> Unlike with the normal stack there is no API for configuring the the shadow
> stack for a new thread, instead the kernel will dynamically allocate a new
> shadow stack with the same size as the normal stack. This appears to be due
> to the shadow stack series having been in development since before the more
> extensible clone3() was added rather than anything more deliberate.
> 
> Add a paramter to clone3() specifying the shadow stack pointer to use
> for the new thread, this is inconsistent with the way we specify the
> normal stack but during review concerns were expressed about having to
> identify where the shadow stack pointer should be placed especially in
> cases where the shadow stack has been previously active.  If no shadow
> stack is specified then the existing implicit allocation behaviour is
> maintained.
> 
> If a shadow stack pointer is specified then it is required to have an
> architecture defined token placed on the stack, this will be consumed by
> the new task.  If no valid token is present then this will be reported
> with -EINVAL.  This token prevents new threads being created pointing at
> the shadow stack of an existing running thread.
> 
> If the architecture does not support shadow stacks the shadow stack
> pointer must be not be specified, architectures that do support the
> feature are expected to enforce the same requirement on individual
> systems that lack shadow stack support.
> 
> Update the existing arm64 and x86 implementations to pay attention to
> the newly added arguments, in order to maintain compatibility we use the
> existing behaviour if no shadow stack is specified. Since we are now
> using more fields from the kernel_clone_args we pass that into the
> shadow stack code rather than individual fields.
> 
> Portions of the x86 architecture code were written by Rick Edgecombe.
> 
> Signed-off-by: Mark Brown <broonie@kernel.org>

Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>

> @@ -101,12 +103,14 @@ struct clone_args {
>  	__aligned_u64 set_tid;
>  	__aligned_u64 set_tid_size;
>  	__aligned_u64 cgroup;
> +	__aligned_u64 shadow_stack_pointer;
>  };
>  #endif
>  
> -#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
> -#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
> -#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
> +#define CLONE_ARGS_SIZE_VER0  64 /* sizeof first published struct */
> +#define CLONE_ARGS_SIZE_VER1  80 /* sizeof second published struct */
> +#define CLONE_ARGS_SIZE_VER2  88 /* sizeof third published struct */
> +#define CLONE_ARGS_SIZE_VER3  96 /* sizeof fourth published struct */

Acked.

Kind regards,
Yury