linux-kernel - [PATCH] x86/speculation/l1tf: fix overflow on l1tf_pfn

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Date:   Mon, 20 Aug 2018 11:58:35 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Cc:     "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, stable@...r.kernel.org,
        Adrian Schroeter <adrian@...e.de>,
        Dominique Leuenberger <dimstar@...e.de>
Subject: [PATCH] x86/speculation/l1tf: fix overflow on 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.

Reported-by: Dominique Leuenberger <dimstar@...e.de>
Reported-by: Adrian Schroeter <adrian@...e.de>
Fixes: 17dbca119312 ("x86/speculation/l1tf: Add sysfs reporting for l1tf")
Fixes: 377eeaa8e11f ("x86/speculation/l1tf: Limit swap file size to MAX_PA/2")
Cc: stable@...r.kernel.org
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 arch/x86/include/asm/processor.h | 4 ++--
 arch/x86/mm/init.c               | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 682286aca881..a0a52274cb4a 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -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);
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index acfab322fbe0..02de3d6065c4 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -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;
 }
-- 
2.18.0