[RFC PATCH v1 15/28] riscv/mm: Implement map_shadow_stack() syscall

[Deepak Gupta]

On Fri, Feb 09, 2024 at 08:44:53PM +0000, Edgecombe, Rick P wrote:
>On Wed, 2024-01-24 at 22:21 -0800, debug at rivosinc.com wrote:
>> From: Deepak Gupta <debug at rivosinc.com>
>>
>> As discussed extensively in the changelog for the addition of this
>> syscall on x86 ("x86/shstk: Introduce map_shadow_stack syscall") the
>> existing mmap() and madvise() syscalls do not map entirely well onto
>> the
>> security requirements for guarded control stacks since they lead to
>> windows where memory is allocated but not yet protected or stacks
>> which
>> are not properly and safely initialised. Instead a new syscall
>> map_shadow_stack() has been defined which allocates and initialises a
>> shadow stack page.
>>
>> This patch implements this syscall for riscv. riscv doesn't require
>> token
>> to be setup by kernel because user mode can do that by itself.
>> However to
>> provide compatiblity and portability with other architectues, user
>> mode can
>> specify token set flag.
>
>A lot of this code look very familiar. We'll have to think about at
>what point we could pull some of it into the code kernel.
>
>I think if we had an arch write_user_shstk(), most of the code could be
>shared here.

Yes it is. I'll think a little bit more on this on next set of patchsets
when I send.