x86, kfence: enable KFENCE for x86

Add architecture specific implementation details for KFENCE and enable
KFENCE for the x86 architecture. In particular, this implements the
required interface in <asm/kfence.h> for setting up the pool and
providing helper functions for protecting and unprotecting pages.

For x86, we need to ensure that the pool uses 4K pages, which is done
using the set_memory_4k() helper function.

[elver@google.com: add missing copyright and description header]
  Link: https://lkml.kernel.org/r/20210118092159.145934-2-elver@google.com

Link: https://lkml.kernel.org/r/20201103175841.3495947-3-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Co-developed-by: Marco Elver <elver@google.com>
Reviewed-by: Jann Horn <jannh@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christopher Lameter <cl@linux.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hillf Danton <hdanton@sina.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joern Engel <joern@purestorage.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: SeongJae Park <sjpark@amazon.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 70 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kfence.h b/arch/x86/include/asm/kfence.h
new file mode 100644
index 000000000000..a0659dbd93ea
--- /dev/null
+++ b/arch/x86/include/asm/kfence.h
@@ -0,0 +1,70 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * x86 KFENCE support.
+ *
+ * Copyright (C) 2020, Google LLC.
+ */
+
+#ifndef _ASM_X86_KFENCE_H
+#define _ASM_X86_KFENCE_H
+
+#include <linux/bug.h>
+#include <linux/kfence.h>
+
+#include <asm/pgalloc.h>
+#include <asm/pgtable.h>
+#include <asm/set_memory.h>
+#include <asm/tlbflush.h>
+
+/*
+ * The page fault handler entry function, up to which the stack trace is
+ * truncated in reports.
+ */
+#define KFENCE_SKIP_ARCH_FAULT_HANDLER "asm_exc_page_fault"
+
+/* Force 4K pages for __kfence_pool. */
+static inline bool arch_kfence_init_pool(void)
+{
+	unsigned long addr;
+
+	for (addr = (unsigned long)__kfence_pool; is_kfence_address((void *)addr);
+	     addr += PAGE_SIZE) {
+		unsigned int level;
+
+		if (!lookup_address(addr, &level))
+			return false;
+
+		if (level != PG_LEVEL_4K)
+			set_memory_4k(addr, 1);
+	}
+
+	return true;
+}
+
+/* Protect the given page and flush TLB. */
+static inline bool kfence_protect_page(unsigned long addr, bool protect)
+{
+	unsigned int level;
+	pte_t *pte = lookup_address(addr, &level);
+
+	if (WARN_ON(!pte || level != PG_LEVEL_4K))
+		return false;
+
+	/*
+	 * We need to avoid IPIs, as we may get KFENCE allocations or faults
+	 * with interrupts disabled. Therefore, the below is best-effort, and
+	 * does not flush TLBs on all CPUs. We can tolerate some inaccuracy;
+	 * lazy fault handling takes care of faults after the page is PRESENT.
+	 */
+
+	if (protect)
+		set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT));
+	else
+		set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
+
+	/* Flush this CPU's TLB. */
+	flush_tlb_one_kernel(addr);
+	return true;
+}
+
+#endif /* _ASM_X86_KFENCE_H */