[PATCH] github: Reduce ASLR entropy to be compatible with asan in llvm 14.

[Aaron Conole]

GitHub recently started using newer Ubuntu 22.04 LTS container images,
versioned 20240310.1.0 which use 32-bit entropy for ASLR:

  $ sudo sysctl -a | grep vm.mmap.rnd
  vm.mmap_rnd_bits = 32
  vm.mmap_rnd_compat_bits = 16

This breaks builds (such as the one at
https://github.com/DPDK/dpdk/actions/runs/8234334617/job/22515850325) by
causing a random segfault when ASAN is used, because older ASAN gets
confused by memory mappings and crashes.

The issue is fixed in newer releases of LLVM:
  https://github.com/llvm/llvm-project/commit/fb77ca05ffb4f8e666878f2f6718a9fb4d686839
  https://reviews.llvm.org/D148280

But these are not available in Ubuntu 22.04 image.

This should be fixed by GitHub, but until new images are available
reducing ASLR entropy manually to 28 bits to make builds work.

Reported-at: https://github.com/actions/runner-images/issues/9491
Signed-off-by: Aaron Conole <aconole at redhat.com>
Suggested-by: Ilya Maximets <i.maximets at ovn.org>
---
 .github/workflows/build.yml | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 776fbf6f30..228aad8289 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -139,6 +139,13 @@ jobs:
         .ci/linux-setup.sh
         # Workaround on $HOME permissions as EAL checks them for plugin loading
         chmod o-w $HOME
+    - name: Reduce ASLR entropy
+      if: env.ASAN == 'true'
+      # Asan in llvm 14 provided in ubuntu-22.04 is incompatible with
+      # high-entropy ASLR configured in much newer kernels that GitHub
+      # runners are using leading to random crashes:
+      #   https://github.com/actions/runner-images/issues/9491
+      run: sudo sysctl -w vm.mmap_rnd_bits=28
     - name: Build and test
       run: .ci/linux-build.sh
     - name: Upload logs on failure
-- 
2.41.0