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fix(usb): a configuration of 9 bytes or less is refused, and a cut one is said (#170, #171)

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After the configuration descriptor's first 9 bytes the event loop asked for
min(wTotalLength, 128) whatever it was. A wTotalLength of 9 or less was then
asked for again as "short" -- for ever, that slot never leaving enumeration
(#170); 0 also issued a zero-length data stage. A set longer than the 128-byte
buffer was cut without a word, its later interfaces never seen (#171).

The decision is usb_config_request_length() (moved out of the event loop,
then fixed): 9 or less is 0 -- "xhci: a configuration of N bytes has no
interface -- not used", and nothing more is asked; longer than the buffer is
cut and said -- "xhci: config of N bytes cut to 128 -- rest unseen" (at most
53 characters). The buffer stays 128 bytes; its size is #171's to rule.

kernel/tests/test_usb_config.c, seen to fail first against the decision as it
was (10 failures: wTotalLength 1 to 9 asked for again, the cut unsaid), now
20 checks, 0 failures. Both runs in logs/20261112-180140/kernel-tests/. Built for amd64,
aarch64 and riscv64; the boots come with the protocol. #171's other box, a
composite device on the SER5, is Captain Bob's.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017RzZgrf7V7Zk2iczBXDRbm
This commit is contained in:
Claude
2026-11-12 18:01:40 +00:00
parent 8b482bedb8
commit a882465573
5 changed files with 43 additions and 1 deletions
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kernel/src/usb/usb_config.c
+12
View File
@@ -10,6 +10,18 @@
#include "starkernel/xhci.h"
#include <string.h>
/* The event loop asked for min(wTotalLength, cap) whatever it was. A wTotalLength of 9 or less was
* then asked for again as "short" (xhci_ep0_get_config_descriptor: length <= 9), for ever (#170),
* and a set longer than the buffer was cut without a word (#171). Now: 9 or less is refused (0),
* and a cut is said. */
uint16_t usb_config_request_length(uint16_t total, uint16_t cap, int *cut)
{
*cut = 0;
if (total <= 9u) return 0; /* no room for anything after the Configuration descriptor */
if (total > cap) { *cut = 1; return cap; }
return total;
}
static uint16_t le16(const uint8_t *p) { return (uint16_t)(p[0] | ((uint16_t)p[1] << 8)); }
void usb_config_parse(const uint8_t *desc, uint16_t len, usb_config_t *out)
kernel/src/usb/xhci.c
+10 -1
View File
@@ -2214,10 +2214,19 @@ static void xhci_poll_one(xhci_dev_t *dev)
case XHCI_XFER_CONFIG_DESC_SHORT: {
uint16_t total_len = (uint16_t)(xms->config_descriptor[USB_CONFIG_OFF_TOTAL_LENGTH] |
((uint16_t)xms->config_descriptor[USB_CONFIG_OFF_TOTAL_LENGTH + 1] << 8));
int cut;
uint16_t want = usb_config_request_length(total_len, (uint16_t)sizeof(xms->config_descriptor), &cut);
xms->config_total_length = total_len;
xhci_log_hex32("xhci: config wTotalLength=", total_len);
if (want == 0) { /* #170: it would be asked for again, for ever */
log_message(LOG_WARN, "xhci: a configuration of %u bytes has no interface -- not used", (unsigned)total_len);
break;
}
if (cut) /* #171: interfaces past the buffer are not seen */
log_message(LOG_WARN, "xhci: config of %u bytes cut to %u -- rest unseen",
(unsigned)total_len, (unsigned)want);
xms->next_action = XHCI_NEXT_ACTION_GET_CONFIG_DESC;
xms->next_action_length = total_len;
xms->next_action_length = want;
break;
}
case XHCI_XFER_CONFIG_DESC_FULL: {