linux-kernel - [PATCHv2 2/2] x86/boot/KASLR: Fix boot with some memory above MAXMEM

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Date:   Mon,  8 Jun 2020 15:54:24 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Tony Luck <tony.luck@...el.com>, x86@...nel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, stable@...r.kernel.org
Subject: [PATCHv2 2/2] x86/boot/KASLR: Fix boot with some memory above MAXMEM

A 5-level paging capable machine can have memory above 46-bit in the
physical address space. This memory is only addressable in the 5-level
paging mode: we don't have enough virtual address space to create direct
mapping for such memory in the 4-level paging mode

Teach KASLR to avoid memory regions above MAXMEM or truncate the region
if the end is above MAXMEM.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reviewed-by: Dave Hansen <dave.hansen@...el.com>
Cc: stable@...r.kernel.org # v4.14
---
 arch/x86/boot/compressed/kaslr.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index d7408af55738..99db18eeb40e 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -695,7 +695,18 @@ static bool process_mem_region(struct mem_vector *region,
 			       unsigned long long minimum,
 			       unsigned long long image_size)
 {
+	unsigned long long end;
 	int i;
+
+	/* Cannot access memory region above MAXMEM: skip it. */
+	if (region->start >= MAXMEM)
+		return 0;
+
+	/* Truncate the region if the end is above MAXMEM */
+	end = region->start + region->size;
+	end = min_t(unsigned long long, end, MAXMEM - 1);
+	region->size = end - region->start;
+
 	/*
 	 * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
 	 * use @region directly.
-- 
2.26.2