linux-hardening - [PATCH v5 1/7] mm: Restore init_on

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Date:   Tue,  9 Mar 2021 13:42:55 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Kees Cook <keescook@...omium.org>, stable@...r.kernel.org,
        Elena Reshetova <elena.reshetova@...el.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Potapenko <glider@...gle.com>,
        Alexander Popov <alex.popov@...ux.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jann Horn <jannh@...gle.com>,
        kernel-hardening@...ts.openwall.com,
        linux-hardening@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: [PATCH v5 1/7] mm: Restore init_on_* static branch defaults

Choosing the initial state of static branches changes the assembly layout
(if the condition is expected to be likely, inline, or unlikely, out of
line via a jump). The _TRUE/_FALSE defines for CONFIG_INIT_ON_*_DEFAULT_ON
were accidentally removed. These need to stay so that the CONFIG controls
the pessimization of the resulting static branch NOP/JMP locations.

Fixes: 04013513cc84 ("mm, page_alloc: do not rely on the order of page_poison and init_on_alloc/free parameters")
Cc: stable@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/mm.h | 8 ++++++++
 mm/page_alloc.c    | 8 ++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 77e64e3eac80..b3317d91ee8e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2871,7 +2871,11 @@ static inline void kernel_poison_pages(struct page *page, int numpages) { }
 static inline void kernel_unpoison_pages(struct page *page, int numpages) { }
 #endif
 
+#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
+DECLARE_STATIC_KEY_TRUE(init_on_alloc);
+#else
 DECLARE_STATIC_KEY_FALSE(init_on_alloc);
+#endif
 static inline bool want_init_on_alloc(gfp_t flags)
 {
 	if (static_branch_unlikely(&init_on_alloc))
@@ -2879,7 +2883,11 @@ static inline bool want_init_on_alloc(gfp_t flags)
 	return flags & __GFP_ZERO;
 }
 
+#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
+DECLARE_STATIC_KEY_TRUE(init_on_free);
+#else
 DECLARE_STATIC_KEY_FALSE(init_on_free);
+#endif
 static inline bool want_init_on_free(void)
 {
 	return static_branch_unlikely(&init_on_free);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3e4b29ee2b1e..f2d474a844cf 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -167,10 +167,18 @@ unsigned long totalcma_pages __read_mostly;
 
 int percpu_pagelist_fraction;
 gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
+#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
+DEFINE_STATIC_KEY_TRUE(init_on_alloc);
+#else
 DEFINE_STATIC_KEY_FALSE(init_on_alloc);
+#endif
 EXPORT_SYMBOL(init_on_alloc);
 
+#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
+DEFINE_STATIC_KEY_TRUE(init_on_free);
+#else
 DEFINE_STATIC_KEY_FALSE(init_on_free);
+#endif
 EXPORT_SYMBOL(init_on_free);
 
 static bool _init_on_alloc_enabled_early __read_mostly
-- 
2.25.1