boot-qemu.sh: Use implementation defined pointer authentication algorithm

By default, QEMU's TCG uses the architected QARMA algorithm for pointer
authentication, which is better cryptographically but extremely slow to
emulate. As of QEMU 6.0.0, there is an "Implementation Defined"
algorithm available, which is not cryptographic but significantly faster
to run.

ARCH=arm64 defconfig:

Benchmark 1: QARMA
  Time (mean ± σ):     10.381 s ±  0.048 s    [User: 8.469 s, System: 0.142 s]
  Range (min … max):   10.317 s … 10.478 s    50 runs

Benchmark 2: Implementation Defined
  Time (mean ± σ):      7.051 s ±  0.015 s    [User: 5.125 s, System: 0.130 s]
  Range (min … max):    7.014 s …  7.083 s    50 runs

Summary
  'Implementation Defined' ran
    1.47 ± 0.01 times faster than 'QARMA'

ARCH=arm64 defconfig + KASAN_SW_TAGS + the KUnit tests:

Benchmark 1: QARMA
  Time (mean ± σ):     185.997 s ±  2.778 s    [User: 184.043 s, System: 0.593 s]
  Range (min … max):   182.816 s … 190.463 s    10 runs

Benchmark 2: Implementation Defined
  Time (mean ± σ):     29.618 s ±  0.301 s    [User: 26.951 s, System: 0.500 s]
  Range (min … max):   29.185 s … 30.103 s    10 runs

Summary
  'Implementation Defined' ran
    6.28 ± 0.11 times faster than 'QARMA'

This should help avoid weird timeouts in CI, as the VMs can be quite
slow.

Aside from the benchmarks above, this change is visible in dmesg:

[    0.000000] CPU features: detected: Address authentication (architected QARMA5 algorithm)

vs.

[    0.000000] CPU features: detected: Address authentication (IMP DEF algorithm)

Link: https://lore.kernel.org/YlgVa+AP0g4IYvzN@lakrids/
Link: https://gitlab.com/qemu-project/qemu/-/blob/v7.0.0/docs/system/arm/cpu-features.rst
Signed-off-by: Nathan Chancellor <[email protected]>

Author: nathanchance

boot-qemu.sh

@@ -232,17 +232,23 @@ function setup_qemu_args() {
             KIMAGE=Image.gz
             QEMU=(qemu-system-aarch64)
             get_full_kernel_path
-            if [[ $(get_qemu_ver_code) -ge 602050 ]]; then
+            QEMU_VER_CODE=$(get_qemu_ver_code)
+            if [[ ${QEMU_VER_CODE} -ge 602050 ]]; then
                 LNX_VER_CODE=$(get_lnx_ver_code gzip -c -d "${KERNEL}")
                 # https://gitlab.com/qemu-project/qemu/-/issues/964
                 if [[ ${LNX_VER_CODE} -lt 416000 ]]; then
                     CPU=cortex-a72
-                # https://gitlab.com/qemu-project/qemu/-/commit/69b2265d5fe8e0f401d75e175e0a243a7d505e53
+                # lpa2=off: https://gitlab.com/qemu-project/qemu/-/commit/69b2265d5fe8e0f401d75e175e0a243a7d505e53
+                # pauth-impdef=true: https://lore.kernel.org/YlgVa+AP0g4IYvzN@lakrids/
                 elif [[ ${LNX_VER_CODE} -lt 512000 ]]; then
-                    CPU=max,lpa2=off
+                    CPU=max,lpa2=off,pauth-impdef=true
                 fi
             fi
-            [[ -z ${CPU} ]] && CPU=max
+            if [[ -z ${CPU} ]]; then
+                CPU=max
+                # https://lore.kernel.org/YlgVa+AP0g4IYvzN@lakrids/
+                [[ ${QEMU_VER_CODE} -ge 600000 ]] && CPU=${CPU},pauth-impdef=true
+            fi
             APPEND_STRING+="console=ttyAMA0 earlycon "
             QEMU_ARCH_ARGS=(
                 -cpu "${CPU}"