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From:   andrey.konovalov@linux.dev
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com, Will Deacon <will@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH mm 2/2] kasan, scs: support tagged vmalloc mappings
Date:   Wed,  2 Mar 2022 16:13:31 +0100
Message-Id: <2f6605e3a358cf64d73a05710cb3da356886ad29.1646233925.git.andreyknvl@google.com>
In-Reply-To: <9230ca3d3e40ffca041c133a524191fd71969a8d.1646233925.git.andreyknvl@google.com>
References: <9230ca3d3e40ffca041c133a524191fd71969a8d.1646233925.git.andreyknvl@google.com>
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From: Andrey Konovalov <andreyknvl@google.com>

Fix up the custom KASAN instrumentation for Shadow Call Stack to support
vmalloc() mappings and pointers being tagged.

- Use the tagged pointer returned by kasan_unpoison_vmalloc() in
  __scs_alloc() when calling memset() to avoid false-positives.

- Do not return a tagged Shadow Call Stack pointer from __scs_alloc(),
  as this might lead to conflicts with the instrumentation.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

Andrew, please put this patch after
"kasan, vmalloc: only tag normal vmalloc allocations".
---
 kernel/scs.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/scs.c b/kernel/scs.c
index 1033a76a3284..b7e1b096d906 100644
--- a/kernel/scs.c
+++ b/kernel/scs.c
@@ -32,16 +32,19 @@ static void *__scs_alloc(int node)
 	for (i = 0; i < NR_CACHED_SCS; i++) {
 		s = this_cpu_xchg(scs_cache[i], NULL);
 		if (s) {
-			kasan_unpoison_vmalloc(s, SCS_SIZE,
-					       KASAN_VMALLOC_PROT_NORMAL);
+			s = kasan_unpoison_vmalloc(s, SCS_SIZE,
+						   KASAN_VMALLOC_PROT_NORMAL);
 			memset(s, 0, SCS_SIZE);
-			return s;
+			goto out;
 		}
 	}
 
-	return __vmalloc_node_range(SCS_SIZE, 1, VMALLOC_START, VMALLOC_END,
+	s = __vmalloc_node_range(SCS_SIZE, 1, VMALLOC_START, VMALLOC_END,
 				    GFP_SCS, PAGE_KERNEL, 0, node,
 				    __builtin_return_address(0));
+
+out:
+	return kasan_reset_tag(s);
 }
 
 void *scs_alloc(int node)
-- 
2.25.1