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Refactor copying data to userspace

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This commit is contained in:
Raoul Strackx 2022-08-10 10:46:27 +02:00
parent 14a459bf37
commit 25de53f768
1 changed files with 32 additions and 19 deletions
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51
library/std/src/sys/sgx/abi/usercalls/alloc.rs
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@ -305,6 +305,34 @@ pub unsafe fn from_raw_parts(ptr: *mut T, len: usize) -> Self {
}
}
// Split a memory region ptr..ptr + len into three parts:
// +--------+
// | small0 | Chunk smaller than 8 bytes
// +--------+
// | big | Chunk 8-byte aligned, and size a multiple of 8 bytes
// +--------+
// | small1 | Chunk smaller than 8 bytes
// +--------+
fn region_as_aligned_chunks(ptr: *const u8, len: usize) -> (u8, usize, u8) {
let small0_size = (8 - ptr as usize % 8) as u8;
let small1_size = ((len - small0_size as usize) % 8) as u8;
let big_size = len - small0_size as usize - small1_size as usize;
(small0_size, big_size, small1_size)
}
unsafe fn copy_quadwords(src: *const u8, dst: *mut u8, len: usize) {
unsafe {
asm!(
"rep movsq (%rsi), (%rdi)",
inout("rcx") len / 8 => _,
inout("rdi") dst => _,
inout("rsi") src => _,
options(att_syntax, nostack, preserves_flags)
);
}
}
/// Copies `len` bytes of data from enclave pointer `src` to userspace `dst`
///
/// This function mitigates stale data vulnerabilities by ensuring all writes to untrusted memory are either:
@ -343,17 +371,6 @@ unsafe fn copy_bytewise_to_userspace(src: *const u8, dst: *mut u8, len: usize) {
}
}
unsafe fn copy_aligned_quadwords_to_userspace(src: *const u8, dst: *mut u8, len: usize) {
unsafe {
asm!(
"rep movsq (%rsi), (%rdi)",
inout("rcx") len / 8 => _,
inout("rdi") dst => _,
inout("rsi") src => _,
options(att_syntax, nostack, preserves_flags)
);
}
}
assert!(!src.is_null());
assert!(!dst.is_null());
assert!(is_enclave_range(src, len));
@ -370,7 +387,7 @@ unsafe fn copy_aligned_quadwords_to_userspace(src: *const u8, dst: *mut u8, len:
} else if len % 8 == 0 && dst as usize % 8 == 0 {
// Copying 8-byte aligned quadwords: copy quad word per quad word
unsafe {
copy_aligned_quadwords_to_userspace(src, dst, len);
copy_quadwords(src, dst, len);
}
} else {
// Split copies into three parts:
@ -381,20 +398,16 @@ unsafe fn copy_aligned_quadwords_to_userspace(src: *const u8, dst: *mut u8, len:
// +--------+
// | small1 | Chunk smaller than 8 bytes
// +--------+
let (small0_size, big_size, small1_size) = region_as_aligned_chunks(dst, len);
unsafe {
// Copy small0
let small0_size = (8 - dst as usize % 8) as u8;
let small0_src = src;
let small0_dst = dst;
copy_bytewise_to_userspace(small0_src as _, small0_dst, small0_size as _);
copy_bytewise_to_userspace(src, dst, small0_size as _);
// Copy big
let small1_size = ((len - small0_size as usize) % 8) as u8;
let big_size = len - small0_size as usize - small1_size as usize;
let big_src = src.offset(small0_size as _);
let big_dst = dst.offset(small0_size as _);
copy_aligned_quadwords_to_userspace(big_src as _, big_dst, big_size);
copy_quadwords(big_src as _, big_dst, big_size);
// Copy small1
let small1_src = src.offset(big_size as isize + small0_size as isize);