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greq/msg: simplify SnpGuestRequestMsgHdr::get_aad_slice() #400

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Jul 3, 2024
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greq/msg: simplify SnpGuestRequestMsgHdr::get_aad_slice() #400

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32 changes: 12 additions & 20 deletions kernel/src/greq/msg.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,9 +13,9 @@ use alloc::{
boxed::Box,
};
use core::{
mem::size_of,
ptr::{addr_of, addr_of_mut},
slice::{from_raw_parts, from_raw_parts_mut, from_ref},
mem::{offset_of, size_of},
ptr::{self, addr_of_mut},
slice::{from_raw_parts, from_raw_parts_mut},
};

use crate::{
Expand Down Expand Up @@ -149,22 +149,15 @@ impl SnpGuestRequestMsgHdr {

/// Get a slice of the header fields used as additional authenticated data (AAD)
fn get_aad_slice(&self) -> &[u8] {
let self_gva = addr_of!(*self);
let algo_gva = addr_of!(self.algo);
let algo_offset = algo_gva as isize - self_gva as isize;

let slice: &[Self] = from_ref(self);
let ptr: *const Self = slice.as_ptr();
// SAFETY: we are doing:
// &[Self] -> *const Self -> *const u8 -> &[u8]
// This is safe as it simply reinterprets the underlying type as bytes
// by using the &self borrow. This is safe because Self has no invalid
// representations, as it is composed of simple integer types.
// &[u8] has no alignment requirements, and this new slice has the
// same size as Self, so we are within bounds.
let b = unsafe { from_raw_parts(ptr.cast::<u8>(), size_of::<Self>()) };

&b[algo_offset as usize..]
let algo_offset = offset_of!(Self, algo);

let ptr = ptr::from_ref(self).cast::<u8>();
// SAFETY: we are simply reinterpreting Self as a slice of bytes. This
// is safe because &[u8] as no alignment requirements and no invalid
// representations, and Self is composed of simple integer types. We
// make sure the resulting byte slice has the same size as Self.
let slice = unsafe { from_raw_parts(ptr, size_of::<Self>()) };
&slice[algo_offset..]
}

/// Get [`SnpGuestRequestMsgHdr`] as a mutable slice reference
Expand Down Expand Up @@ -481,7 +474,6 @@ impl SnpGuestRequestExtData {
mod tests {
use super::*;
use crate::mm::alloc::{TestRootMem, DEFAULT_TEST_MEMORY_SIZE};
use core::mem::offset_of;

#[test]
fn test_snp_guest_request_hdr_offsets() {
Expand Down
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