pkg/vcs: apply more backports to Linux

Factor out the code that cherry-picks missing fixes to a Linux repo.

Add two more commits that address issues with older kernel revisions.

2 files changed, 74 insertions, 16 deletions

diff --git a/pkg/vcs/linux.go b/pkg/vcs/linux.go
index 341e488f4..16e1c79fa 100644
--- a/pkg/vcs/linux.go
+++ b/pkg/vcs/linux.go
@@ -167,24 +167,10 @@ func (ctx *linux) EnvForCommit(
 		Compiler:     compiler,
 		KernelConfig: cf.Serialize(),
 	}
-
-	// Compiling v4.6..v5.11 with a modern objtool, w/o this patch, results in the
-	// following issue, when compiling with clang:
-	// arch/x86/entry/thunk_64.o: warning: objtool: missing symbol table
-	// We don't bisect that far back with neither clang nor gcc, so this should be fine:
-	fix := "1d489151e9f9d1647110277ff77282fe4d96d09b"
-	fixTitle := "objtool: Don't fail on missing symbol table"
-	searchResult, err := ctx.git.GetCommitByTitle(fixTitle)
+	err = linuxFixBackports(ctx.git)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to cherry pick fixes: %w", err)
 	}
-	if searchResult == nil {
-		_, err := ctx.git.git("cherry-pick", "--no-commit", fix)
-		if err != nil {
-			return nil, err
-		}
-	}
-
 	return env, nil
 }
 
diff --git a/pkg/vcs/linux_patches.go b/pkg/vcs/linux_patches.go
new file mode 100644
index 000000000..868bbf4c0
--- /dev/null
+++ b/pkg/vcs/linux_patches.go
@@ -0,0 +1,72 @@
+// Copyright 2023 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package vcs
+
+// BackportCommit describes a fix commit that must be cherry-picked to an older
+// kernel revision in order to enable kernel build / boot.
+type BackportCommit struct {
+	// If non-empty, it will be first ensured that this commit is reachable.
+	GuiltyTitle string `json:"guilty_title"`
+	// The hash of the commit to cherry-pick.
+	FixHash string `json:"fix_hash"`
+	// The title of the commit to cherry-pick.
+	// It's used to determine whether the fix is already in place.
+	FixTitle string `json:"fix_title"`
+}
+
+// linuxFixBackports() cherry-picks the commits necessary to compile/run older Linux kernel releases.
+func linuxFixBackports(repo *git, extraCommits ...BackportCommit) error {
+	list := append([]BackportCommit{}, pickLinuxCommits...)
+	for _, info := range append(list, extraCommits...) {
+		if info.GuiltyTitle != "" {
+			guiltyCommit, err := repo.GetCommitByTitle(info.GuiltyTitle)
+			if err != nil {
+				return err
+			}
+			if guiltyCommit == nil {
+				// The problem is not yet introduced.
+				continue
+			}
+		}
+		fixCommit, err := repo.GetCommitByTitle(info.FixTitle)
+		if err != nil {
+			return err
+		}
+		if fixCommit != nil {
+			// The fix is already present.
+			continue
+		}
+		_, err = repo.git("cherry-pick", "--no-commit", info.FixHash)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+var pickLinuxCommits = []BackportCommit{
+	{
+		// Compiling v4.6..v5.11 with a modern objtool, w/o this patch, results in the
+		// following issue, when compiling with clang:
+		// arch/x86/entry/thunk_64.o: warning: objtool: missing symbol table
+		// We don't bisect that far back with neither clang nor gcc, so this should be fine:
+		FixHash:  `1d489151e9f9d1647110277ff77282fe4d96d09b`,
+		FixTitle: `objtool: Don't fail on missing symbol table`,
+	},
+	{
+		// In newer compiler versions, kernel compilation fails with:
+		// subcmd-util.h:56:23: error: pointer may be used after ‘realloc’ [-Werror=use-after-free]
+		// 56 |                 ret = realloc(ptr, size);
+		GuiltyTitle: `perf tools: Finalize subcmd independence`,
+		FixHash:     `52a9dab6d892763b2a8334a568bd4e2c1a6fde66`,
+		FixTitle:    `libsubcmd: Fix use-after-free for realloc(..., 0)`,
+	},
+	{
+		// A number of old releases fail with KASAN: use-after-free in task_active_pid_ns.
+		// The problem was actually present so long ago that we do not need to check whether
+		// the guilty commit is present. We don't bisect that back (v2.*) anyway.
+		FixHash:  `0711f0d7050b9e07c44bc159bbc64ac0a1022c7f`,
+		FixTitle: "pid: take a reference when initializing `cad_pid`",
+	},
+}