Commit b569c184 authored Mar 08, 2019 by Baoquan He Committed by Thomas Gleixner Apr 05, 2019

x86/mm/KASLR: Reduce randomization granularity for 5-level paging to 1GB



The current randomization granularity of 5-level is 512 GB. The mapping of
the real mode trampoline has been reduced to one PUD entry, so there is no
restriction anymore.

Reduce the granularity to 1GB for 5-level paging mode which allows better
randomization.

[ tglx: Massaged changelog ]

Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: dave.hansen@linux.intel.com
Cc: luto@kernel.org
Cc: peterz@infradead.org
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: keescook@chromium.org
Cc: thgarnie@google.com
Link: https://lkml.kernel.org/r/20190308025616.21440-3-bhe@redhat.com

parent 0925dda5

arch/x86/mm/kaslr.c

+2 −8

Original line number	Diff line number	Diff line
		@@ -125,9 +125,6 @@ void __init kernel_randomize_memory(void)
		*/
		entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
		prandom_bytes_state(&rand_state, &rand, sizeof(rand));
		if (pgtable_l5_enabled())
		entropy = (rand % (entropy + 1)) & P4D_MASK;
		else
		entropy = (rand % (entropy + 1)) & PUD_MASK;
		vaddr += entropy;
		*kaslr_regions[i].base = vaddr;
		@@ -137,9 +134,6 @@ void __init kernel_randomize_memory(void)
		* randomization alignment.
		*/
		vaddr += get_padding(&kaslr_regions[i]);
		if (pgtable_l5_enabled())
		vaddr = round_up(vaddr + 1, P4D_SIZE);
		else
		vaddr = round_up(vaddr + 1, PUD_SIZE);
		remain_entropy -= entropy;
		}

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