linux-kernel - [PATCH 4.19 044/101] arm64: kaslr: Reserve size of ARM64_MEMSTART

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Date:   Mon, 15 Apr 2019 20:58:42 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        liyueyi <liyueyi@...e.com>, Will Deacon <will.deacon@....com>,
        "Sasha Levin (Microsoft)" <sashal@...nel.org>
Subject: [PATCH 4.19 044/101] arm64: kaslr: Reserve size of ARM64_MEMSTART_ALIGN in linear region

[ Upstream commit c8a43c18a97845e7f94ed7d181c11f41964976a2 ]

When KASLR is enabled (CONFIG_RANDOMIZE_BASE=y), the top 4K of kernel
virtual address space may be mapped to physical addresses despite being
reserved for ERR_PTR values.

Fix the randomization of the linear region so that we avoid mapping the
last page of the virtual address space.

Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Signed-off-by: liyueyi <liyueyi@...e.com>
[will: rewrote commit message; merged in suggestion from Ard]
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Sasha Levin (Microsoft) <sashal@...nel.org>
---
 arch/arm64/mm/init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 787e27964ab9..774c3e17c798 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -450,7 +450,7 @@ void __init arm64_memblock_init(void)
 		 * memory spans, randomize the linear region as well.
 		 */
 		if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
-			range = range / ARM64_MEMSTART_ALIGN + 1;
+			range /= ARM64_MEMSTART_ALIGN;
 			memstart_addr -= ARM64_MEMSTART_ALIGN *
 					 ((range * memstart_offset_seed) >> 16);
 		}
-- 
2.19.1