linux-kernel - [PATCH 2/2] x86/boot: increase maximum number of avoided KASLR regions

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Message-Id: <1548866403-13390-2-git-send-email-js@alien8.de>
Date:   Wed, 30 Jan 2019 17:40:03 +0100
From:   Julian Stecklina <js@...en8.de>
To:     x86@...nel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, linux-kernel@...r.kernel.org, jschoenh@...zon.de,
        Julian Stecklina <jsteckli@...zon.de>
Subject: [PATCH 2/2] x86/boot: increase maximum number of avoided KASLR regions

From: Julian Stecklina <jsteckli@...zon.de>

The boot code has a limit of 4 "non-standard" regions to avoid for
KASLR. This limit is easy to reach when supplying memmap= parameters to
the kernel. In this case, KASLR would be disabled.

Increase the limit to avoid turning off KASLR even when the user is
heavily manipulating the memory map.

Signed-off-by: Julian Stecklina <jsteckli@...zon.de>
---
 arch/x86/boot/compressed/kaslr.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 5657e34..f078d60 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -92,8 +92,8 @@ struct mem_vector {
 	unsigned long long size;
 };
 
-/* Only supporting at most 4 unusable memmap regions with kaslr */
-#define MAX_MEMMAP_REGIONS	4
+/* Only supporting at most this many unusable memmap regions with kaslr */
+#define MAX_MEMMAP_REGIONS	16
 
 static bool memmap_too_large;
 
@@ -213,7 +213,7 @@ static void mem_avoid_memmap(char *str)
 		i++;
 	}
 
-	/* More than 4 memmaps, fail kaslr */
+	/* Can't store all regions, fail kaslr */
 	if ((i >= MAX_MEMMAP_REGIONS) && str)
 		memmap_too_large = true;
 }
-- 
2.7.4