Commit 9df95169 authored Aug 20, 2018 by Vlastimil Babka Committed by Thomas Gleixner Aug 20, 2018

x86/speculation/l1tf: Fix overflow in l1tf_pfn_limit() on 32bit



On 32bit PAE kernels on 64bit hardware with enough physical bits,
l1tf_pfn_limit() will overflow unsigned long. This in turn affects
max_swapfile_size() and can lead to swapon returning -EINVAL. This has been
observed in a 32bit guest with 42 bits physical address size, where
max_swapfile_size() overflows exactly to 1 << 32, thus zero, and produces
the following warning to dmesg:

[    6.396845] Truncating oversized swap area, only using 0k out of 2047996k

Fix this by using unsigned long long instead.

Fixes: 17dbca11 ("x86/speculation/l1tf: Add sysfs reporting for l1tf")
Fixes: 377eeaa8 ("x86/speculation/l1tf: Limit swap file size to MAX_PA/2")
Reported-by: Dominique Leuenberger <dimstar@suse.de>
Reported-by: Adrian Schroeter <adrian@suse.de>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180820095835.5298-1-vbabka@suse.cz

parent dc76803e

arch/x86/include/asm/processor.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -181,9 +181,9 @@ extern const struct seq_operations cpuinfo_op;

		extern void cpu_detect(struct cpuinfo_x86 *c);

		static inline unsigned long l1tf_pfn_limit(void)
		static inline unsigned long long l1tf_pfn_limit(void)
		{
		return BIT(boot_cpu_data.x86_phys_bits - 1 - PAGE_SHIFT) - 1;
		return BIT_ULL(boot_cpu_data.x86_phys_bits - 1 - PAGE_SHIFT) - 1;
		}

		extern void early_cpu_init(void);

arch/x86/mm/init.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -923,7 +923,7 @@ unsigned long max_swapfile_size(void)

		if (boot_cpu_has_bug(X86_BUG_L1TF)) {
		/* Limit the swap file size to MAX_PA/2 for L1TF workaround */
		unsigned long l1tf_limit = l1tf_pfn_limit() + 1;
		unsigned long long l1tf_limit = l1tf_pfn_limit() + 1;
		/*
		* We encode swap offsets also with 3 bits below those for pfn
		* which makes the usable limit higher.
		@@ -931,7 +931,7 @@ unsigned long max_swapfile_size(void)
		#if CONFIG_PGTABLE_LEVELS > 2
		l1tf_limit <<= PAGE_SHIFT - SWP_OFFSET_FIRST_BIT;
		#endif
		pages = min_t(unsigned long, l1tf_limit, pages);
		pages = min_t(unsigned long long, l1tf_limit, pages);
		}
		return pages;
		}

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