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Add checks and tests for computing abs(offset_bytes)

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The previous code paniced if offset_bytes == i64::MIN. This commit:
  - Properly computes the absoulte value to avoid this panic
  - Adds a test for this edge case

Signed-off-by: Joe Richey <joerichey@google.com>
This commit is contained in:
Joe Richey 2020-05-26 02:00:02 -07:00
parent 6367b544b7
commit 71ef8414bd
3 changed files with 22 additions and 3 deletions
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5
src/librustc_mir/interpret/intrinsics.rs
View file

@ -7,7 +7,7 @@ use std::convert::TryFrom;
use rustc_hir::def_id::DefId;
use rustc_middle::mir::{
self,
interpret::{ConstValue, GlobalId, InterpResult, Scalar},
interpret::{uabs, ConstValue, GlobalId, InterpResult, Scalar},
BinOp,
};
use rustc_middle::ty;
@ -438,6 +438,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
pointee_ty: Ty<'tcx>,
offset_count: i64,
) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
// We cannot overflow i64 as a type's size must be <= isize::MAX.
let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
// The computed offset, in bytes, cannot overflow an isize.
let offset_bytes = offset_count
@ -450,7 +451,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// memory between these pointers must be accessible. Note that we do not require the
// pointers to be properly aligned (unlike a read/write operation).
let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
let size = offset_bytes.checked_abs().unwrap();
let size: u64 = uabs(offset_bytes);
// This call handles checking for integer/NULL pointers.
self.memory.check_ptr_access_align(
min_ptr,

3
src/test/ui/consts/offset_ub.rs
View file

@ -19,4 +19,7 @@ pub const DANGLING: *const u8 = unsafe { ptr::NonNull::<u8>::dangling().as_ptr()
// Right now, a zero offset from null is UB
pub const NULL_OFFSET_ZERO: *const u8 = unsafe { ptr::null::<u8>().offset(0) }; //~NOTE
// Make sure that we don't panic when computing abs(offset*size_of::<T>())
pub const UNDERFLOW_ABS: *const u8 = unsafe { (usize::MAX as *const u8).offset(isize::MIN) }; //~NOTE
fn main() {}

17
src/test/ui/consts/offset_ub.stderr
View file

@ -150,5 +150,20 @@ LL | intrinsics::offset(self, count)
LL | pub const NULL_OFFSET_ZERO: *const u8 = unsafe { ptr::null::<u8>().offset(0) };
| -------------------------------------------------------------------------------
error: aborting due to 10 previous errors
error: any use of this value will cause an error
--> $SRC_DIR/libcore/ptr/const_ptr.rs:LL:COL
|
LL | intrinsics::offset(self, count)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| unable to turn bytes into a pointer
| inside `std::ptr::const_ptr::<impl *const u8>::offset` at $SRC_DIR/libcore/ptr/const_ptr.rs:LL:COL
| inside `UNDERFLOW_ABS` at $DIR/offset_ub.rs:23:47
|
::: $DIR/offset_ub.rs:23:1
|
LL | pub const UNDERFLOW_ABS: *const u8 = unsafe { (usize::MAX as *const u8).offset(isize::MIN) };
| ---------------------------------------------------------------------------------------------
error: aborting due to 11 previous errors