linux-kernel - [PATCH AUTOSEL 5.2 39/42] arm64: consider stack randomization for mmap base only when necessary

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Date:   Sun, 29 Sep 2019 13:32:38 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Alexandre Ghiti <alex@...ti.fr>,
        Catalin Marinas <catalin.marinas@....com>,
        Kees Cook <keescook@...omium.org>,
        Christoph Hellwig <hch@....de>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        James Hogan <jhogan@...nel.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Burton <paul.burton@...s.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.2 39/42] arm64: consider stack randomization for mmap base only when necessary

From: Alexandre Ghiti <alex@...ti.fr>

[ Upstream commit e8d54b62c55ab6201de6d195fc2c276294c1f6ae ]

Do not offset mmap base address because of stack randomization if current
task does not want randomization.  Note that x86 already implements this
behaviour.

Link: http://lkml.kernel.org/r/20190730055113.23635-4-alex@ghiti.fr
Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
Acked-by: Catalin Marinas <catalin.marinas@....com>
Acked-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
Cc: Albert Ou <aou@...s.berkeley.edu>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Christoph Hellwig <hch@...radead.org>
Cc: James Hogan <jhogan@...nel.org>
Cc: Palmer Dabbelt <palmer@...ive.com>
Cc: Paul Burton <paul.burton@...s.com>
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: Russell King <linux@...linux.org.uk>
Cc: Will Deacon <will.deacon@....com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/arm64/mm/mmap.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index b050641b51392..8dac7110f0cb5 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -54,7 +54,11 @@ unsigned long arch_mmap_rnd(void)
 static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
 {
 	unsigned long gap = rlim_stack->rlim_cur;
-	unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + stack_guard_gap;
+	unsigned long pad = stack_guard_gap;
+
+	/* Account for stack randomization if necessary */
+	if (current->flags & PF_RANDOMIZE)
+		pad += (STACK_RND_MASK << PAGE_SHIFT);
 
 	/* Values close to RLIM_INFINITY can overflow. */
 	if (gap + pad > gap)
-- 
2.20.1