gpu: nova-core: gsp: fix undefined behavior in command queue code (8e6c3478) · Commits · git / linux-net

drivers/gpu/nova-core/gsp/cmdq.rs

+68 −46

Original line number	Diff line number	Diff line
		@@ -17,6 +17,7 @@
		},
		new_mutex,
		prelude::*,
		ptr,
		sync::{
		aref::ARef,
		Mutex, //
		@@ -255,37 +256,46 @@ fn new(dev: &device::Device<device::Bound>) -> Result<Self> {
		/// As the message queue is a circular buffer, the region may be discontiguous in memory. In
		/// that case the second slice will have a non-zero length.
		fn driver_write_area(&mut self) -> (&mut [[u8; GSP_PAGE_SIZE]], &mut [[u8; GSP_PAGE_SIZE]]) {
		let tx = self.cpu_write_ptr() as usize;
		let rx = self.gsp_read_ptr() as usize;
		let tx = self.cpu_write_ptr();
		let rx = self.gsp_read_ptr();

		// SAFETY:
		// - We will only access the driver-owned part of the shared memory.
		// - Per the safety statement of the function, no concurrent access will be performed.
		let gsp_mem = unsafe { &mut *self.0.as_mut() };
		// PANIC: per the invariant of `cpu_write_ptr`, `tx` is `< MSGQ_NUM_PAGES`.
		let (before_tx, after_tx) = gsp_mem.cpuq.msgq.data.split_at_mut(tx);

		// The area starting at `tx` and ending at `rx - 2` modulo MSGQ_NUM_PAGES, inclusive,
		// belongs to the driver for writing.

		if rx == 0 {
		// Since `rx` is zero, leave an empty slot at end of the buffer.
		let last = after_tx.len() - 1;
		(&mut after_tx[..last], &mut [])
		// Pointer to the first entry of the CPU message queue.
		let data = ptr::project!(mut self.0.as_mut_ptr(), .cpuq.msgq.data[0]);

		let (tail_end, wrap_end) = if rx == 0 {
		// The write area is non-wrapping, and stops at the second-to-last entry of the command
		// queue (to leave the last one empty).
		(MSGQ_NUM_PAGES - 1, 0)
		} else if rx <= tx {
		// The area is discontiguous and we leave an empty slot before `rx`.
		// PANIC:
		// - The index `rx - 1` is non-negative because `rx != 0` in this branch.
		// - The index does not exceed `before_tx.len()` (which equals `tx`) because
		// `rx <= tx` in this branch.
		(after_tx, &mut before_tx[..(rx - 1)])
		// The write area wraps and continues until `rx - 1`.
		(MSGQ_NUM_PAGES, rx - 1)
		} else {
		// The area is contiguous and we leave an empty slot before `rx`.
		// PANIC:
		// - The index `rx - tx - 1` is non-negative because `rx > tx` in this branch.
		// - The index does not exceed `after_tx.len()` (which is `MSGQ_NUM_PAGES - tx`)
		// because `rx < MSGQ_NUM_PAGES` by the `gsp_read_ptr` invariant.
		(&mut after_tx[..(rx - tx - 1)], &mut [])
		// The write area doesn't wrap and stops at `rx - 1`.
		(rx - 1, 0)
		};

		// SAFETY:
		// - `data` was created from a valid pointer, and `rx` and `tx` are in the
		// `0..MSGQ_NUM_PAGES` range per the invariants of `cpu_write_ptr` and `gsp_read_ptr`,
		// thus the created slices are valid.
		// - The area starting at `tx` and ending at `rx - 2` modulo `MSGQ_NUM_PAGES`,
		// inclusive, belongs to the driver for writing and is not accessed concurrently by
		// the GSP.
		// - The caller holds a reference to `self` for as long as the returned slices are live,
		// meaning the CPU write pointer cannot be advanced and thus that the returned area
		// remains exclusive to the CPU for the duration of the slices.
		// - The created slices point to non-overlapping sub-ranges of `data` in all
		// branches (in the `rx <= tx` case, the second slice ends at `rx - 1` which is strictly
		// less than `tx` where the first slice starts; in the other cases the second slice is
		// empty), so creating two `&mut` references from them does not violate aliasing rules.
		unsafe {
		(
		core::slice::from_raw_parts_mut(
		data.add(num::u32_as_usize(tx)),
		num::u32_as_usize(tail_end - tx),
		),
		core::slice::from_raw_parts_mut(data, num::u32_as_usize(wrap_end)),
		)
		}
		}

		@@ -308,26 +318,38 @@ fn driver_write_area_size(&self) -> usize {
		/// As the message queue is a circular buffer, the region may be discontiguous in memory. In
		/// that case the second slice will have a non-zero length.
		fn driver_read_area(&self) -> (&[[u8; GSP_PAGE_SIZE]], &[[u8; GSP_PAGE_SIZE]]) {
		let tx = self.gsp_write_ptr() as usize;
		let rx = self.cpu_read_ptr() as usize;
		let tx = self.gsp_write_ptr();
		let rx = self.cpu_read_ptr();

		// SAFETY:
		// - We will only access the driver-owned part of the shared memory.
		// - Per the safety statement of the function, no concurrent access will be performed.
		let gsp_mem = unsafe { &*self.0.as_ptr() };
		let data = &gsp_mem.gspq.msgq.data;

		// The area starting at `rx` and ending at `tx - 1` modulo MSGQ_NUM_PAGES, inclusive,
		// belongs to the driver for reading.
		// PANIC:
		// - per the invariant of `cpu_read_ptr`, `rx < MSGQ_NUM_PAGES`
		// - per the invariant of `gsp_write_ptr`, `tx < MSGQ_NUM_PAGES`
		if rx <= tx {
		// The area is contiguous.
		(&data[rx..tx], &[])
		// Pointer to the first entry of the GSP message queue.
		let data = ptr::project!(self.0.as_ptr(), .gspq.msgq.data[0]);

		let (tail_end, wrap_end) = if rx <= tx {
		// Read area is non-wrapping and stops right before `tx`.
		(tx, 0)
		} else {
		// The area is discontiguous.
		(&data[rx..], &data[..tx])
		// Read area is wrapping and stops right before `tx`.
		(MSGQ_NUM_PAGES, tx)
		};

		// SAFETY:
		// - `data` was created from a valid pointer, and `rx` and `tx` are in the
		// `0..MSGQ_NUM_PAGES` range per the invariants of `gsp_write_ptr` and `cpu_read_ptr`,
		// thus the created slices are valid.
		// - The area starting at `rx` and ending at `tx - 1` modulo `MSGQ_NUM_PAGES`,
		// inclusive, belongs to the driver for reading and is not accessed concurrently by
		// the GSP.
		// - The caller holds a reference to `self` for as long as the returned slices are live,
		// meaning the CPU read pointer cannot be advanced and thus that the returned area
		// remains exclusive to the CPU for the duration of the slices.
		unsafe {
		(
		core::slice::from_raw_parts(
		data.add(num::u32_as_usize(rx)),
		num::u32_as_usize(tail_end - rx),
		),
		core::slice::from_raw_parts(data, num::u32_as_usize(wrap_end)),
		)
		}
		}