In xhci_get_port_bandwidth(), we use a variable-length array to
construct the buffer to send back to the guest. Avoid the VLA
by using dma_memory_set() to directly request the memory system
to fill the guest memory with a string of '80's.
The codebase has very few VLAs, and if we can get rid of them all we
can make the compiler error on new additions. This is a defensive
measure against security bugs where an on-stack dynamic allocation
isn't correctly size-checked (e.g. CVE-2021-3527).
Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
---
Use of dma_memory_set() is a suggestion from RTH from Philippe's
original attempt. If we ever do anything about the "use real
values" TODO we'll need to do something else (eg heap-allocated
array), but since we haven't done so since the code was written
in 2012 it doesn't seem very likely we'll ever do so.
---
hw/usb/hcd-xhci.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
index b89b618ec21..324177ad5df 100644
--- a/hw/usb/hcd-xhci.c
+++ b/hw/usb/hcd-xhci.c
@@ -2434,7 +2434,6 @@ static void xhci_detach_slot(XHCIState *xhci, USBPort
*uport)
static TRBCCode xhci_get_port_bandwidth(XHCIState *xhci, uint64_t pctx)
{
dma_addr_t ctx;
- uint8_t bw_ctx[xhci->numports+1];
DPRINTF("xhci_get_port_bandwidth()\n");
@@ -2442,11 +2441,10 @@ static TRBCCode xhci_get_port_bandwidth(XHCIState
*xhci, uint64_t pctx)
DPRINTF("xhci: bandwidth context at "DMA_ADDR_FMT"\n", ctx);
- /* TODO: actually implement real values here */
- bw_ctx[0] = 0;
- memset(&bw_ctx[1], 80, xhci->numports); /* 80% */
- if (dma_memory_write(xhci->as, ctx, bw_ctx, sizeof(bw_ctx),
- MEMTXATTRS_UNSPECIFIED) != MEMTX_OK) {
+ /* TODO: actually implement real values here. This is 80% for all ports. */
+ if (stb_dma(xhci->as, ctx, 0, MEMTXATTRS_UNSPECIFIED) != MEMTX_OK ||
+ dma_memory_set(xhci->as, ctx + 1, 80, xhci->numports,
+ MEMTXATTRS_UNSPECIFIED) != MEMTX_OK) {
qemu_log_mask(LOG_GUEST_ERROR, "%s: DMA memory write failed!\n",
__func__);
return CC_TRB_ERROR;
--
2.34.1
