@@ -712,7 +712,7 @@ static int drm_panic_get_qr_code_url(u8 **qr_image)
char *kmsg;
int max_qr_data_size, url_len;
- url_len = snprintf(url, sizeof(url), CONFIG_DRM_PANIC_SCREEN_QR_CODE_URL "?a=%s&v=%s&zl=",
+ url_len = snprintf(url, sizeof(url), CONFIG_DRM_PANIC_SCREEN_QR_CODE_URL "?a=%s&v=%s&z=",
utsname()->machine, utsname()->release);
max_qr_data_size = drm_panic_qr_max_data_size(panic_qr_version, url_len);
@@ -13,12 +13,13 @@
//! The binary data must be a valid URL parameter, so the easiest way is
//! to use base64 encoding. But this wastes 25% of data space, so the
//! whole stack trace won't fit in the QR code. So instead it encodes
-//! every 13bits of input into 4 decimal digits, and then uses the
+//! every 7 bytes of input into 17 decimal digits, and then uses the
//! efficient numeric encoding, that encode 3 decimal digits into
-//! 10bits. This makes 39bits of compressed data into 12 decimal digits,
-//! into 40bits in the QR code, so wasting only 2.5%. And the numbers are
+//! 10bits. This makes 168bits of compressed data into 51 decimal digits,
+//! into 170bits in the QR code, so wasting only 1.17%. And the numbers are
//! valid URL parameter, so the website can do the reverse, to get the
-//! binary data.
+//! binary data. This is the same algorithm used by Fido v2.2 QR-initiated
+//! authentication specification.
//!
//! Inspired by these 3 projects, all under MIT license:
//!
@@ -26,7 +27,6 @@
//! * <https://github.com/erwanvivien/fast_qr>
//! * <https://github.com/bjguillot/qr>
-use core::cmp;
use kernel::str::CStr;
#[derive(Debug, Clone, Copy, PartialEq, Eq, Ord, PartialOrd)]
@@ -296,35 +296,11 @@ fn version_info(&self) -> u32 {
/// Padding bytes.
const PADDING: [u8; 2] = [236, 17];
-/// Get the next 13 bits of data, starting at specified offset (in bits).
-fn get_next_13b(data: &[u8], offset: usize) -> Option<(u16, usize)> {
- if offset < data.len() * 8 {
- let size = cmp::min(13, data.len() * 8 - offset);
- let byte_off = offset / 8;
- let bit_off = offset % 8;
- // `b` is 20 at max (`bit_off` <= 7 and `size` <= 13).
- let b = (bit_off + size) as u16;
-
- let first_byte = (data[byte_off] << bit_off >> bit_off) as u16;
-
- let number = match b {
- 0..=8 => first_byte >> (8 - b),
- 9..=16 => (first_byte << (b - 8)) + (data[byte_off + 1] >> (16 - b)) as u16,
- _ => {
- (first_byte << (b - 8))
- + ((data[byte_off + 1] as u16) << (b - 16))
- + (data[byte_off + 2] >> (24 - b)) as u16
- }
- };
- Some((number, size))
- } else {
- None
- }
-}
-
/// Number of bits to encode characters in numeric mode.
const NUM_CHARS_BITS: [usize; 4] = [0, 4, 7, 10];
-const POW10: [u16; 4] = [1, 10, 100, 1000];
+/// Number of decimal digits required to encode n bytes of binary data.
+/// eg: you need 15 decimal digits to fit 6 bytes of binary data.
+const BYTES_TO_DIGITS: [usize; 8] = [0, 3, 5, 8, 10, 13, 15, 17];
enum Segment<'a> {
Numeric(&'a [u8]),
@@ -360,13 +336,9 @@ fn character_count(&self) -> usize {
match self {
Segment::Binary(data) => data.len(),
Segment::Numeric(data) => {
- let data_bits = data.len() * 8;
- let last_chars = match data_bits % 13 {
- 1 => 1,
- k => (k + 1) / 3,
- };
- // 4 decimal numbers per 13bits + remainder.
- 4 * (data_bits / 13) + last_chars
+ let last_chars = BYTES_TO_DIGITS[data.len() % 7];
+ // 17 decimal numbers per 7bytes + remainder.
+ 17 * (data.len() / 7) + last_chars
}
}
}
@@ -403,7 +375,7 @@ fn iter(&self) -> SegmentIterator<'_> {
struct SegmentIterator<'a> {
segment: &'a Segment<'a>,
offset: usize,
- carry: u16,
+ carry: u64,
carry_len: usize,
}
@@ -422,40 +394,26 @@ fn next(&mut self) -> Option<Self::Item> {
}
}
Segment::Numeric(data) => {
- if self.carry_len == 3 {
- let out = (self.carry, NUM_CHARS_BITS[self.carry_len]);
- self.carry_len = 0;
- self.carry = 0;
- Some(out)
- } else if let Some((bits, size)) = get_next_13b(data, self.offset) {
- self.offset += size;
- let new_chars = match size {
- 1 => 1,
- k => (k + 1) / 3,
- };
- if self.carry_len + new_chars > 3 {
- self.carry_len = new_chars + self.carry_len - 3;
- let out = (
- self.carry * POW10[new_chars - self.carry_len]
- + bits / POW10[self.carry_len],
- NUM_CHARS_BITS[3],
- );
- self.carry = bits % POW10[self.carry_len];
- Some(out)
- } else {
- let out = (
- self.carry * POW10[new_chars] + bits,
- NUM_CHARS_BITS[self.carry_len + new_chars],
- );
- self.carry_len = 0;
- Some(out)
+ if self.carry_len < 3 && self.offset < data.len() {
+ let mut buf = [0u8; 8];
+ let len = 7.min(data.len() - self.offset);
+ buf[..len].copy_from_slice(&data[self.offset..self.offset + len]);
+ let chunk = u64::from_le_bytes(buf);
+ let pow = u64::pow(10, BYTES_TO_DIGITS[len] as u32);
+ self.carry = chunk + self.carry * pow;
+ self.offset += len;
+ self.carry_len += BYTES_TO_DIGITS[len];
+ }
+ match self.carry_len {
+ 0 => None,
+ len => {
+ let out_len = 3.min(len);
+ self.carry_len -= out_len;
+ let pow = u64::pow(10, self.carry_len as u32);
+ let out = (self.carry / pow) as u16;
+ self.carry = self.carry % pow;
+ Some((out, NUM_CHARS_BITS[out_len]))
}
- } else if self.carry_len > 0 {
- let out = (self.carry, NUM_CHARS_BITS[self.carry_len]);
- self.carry_len = 0;
- Some(out)
- } else {
- None
}
}
}
The current encoding, is done by converting 13bits of input into 4 decimal digits, that are then encoded efficiently using the numeric encoding of the QR code specification. The Fido v2.2 specification [1] uses a similar approach for its QR-initiated authentication. The only difference is that it converts 7 bytes (56bits) of input into 17 decimal digits. The benefit is that the algorithm doesn't require to split input bytes into 13bits chunk, and the ratio is a bit better. This improvement was proposed by Jó Ágila Bitsch in [2]. drm_panic is still young, and the QR code feature is not widely used, so it's still time to switch to a common algorithm, shared with a widely used standard. I also changed the name of the url parameter, from zl= to z=, so the website can keep backward compatibility if needed. [1] https://fidoalliance.org/specs/fido-v2.2-rd-20230321/fido-client-to-authenticator-protocol-v2.2-rd-20230321.html#hybrid-qr-initiated [2] https://github.com/kdj0c/panic_report/issues/2 Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com> --- drivers/gpu/drm/drm_panic.c | 2 +- drivers/gpu/drm/drm_panic_qr.rs | 104 ++++++++++---------------------- 2 files changed, 32 insertions(+), 74 deletions(-) base-commit: c6eabbab359c156669e10d5dec3e71e80ff09bd2