Eric Lee / smarc-fsl-linux-kernel

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Commit 0a46fff2f9108c2c44218380a43a736cf4612541

Authored by Kirill A. Shutemov
Committed by Borislav Petkov
1 parent f897e60a12

x86/boot/compressed/64: Fix boot on machines with broken E820 table 

BIOS on Samsung 500C Chromebook reports very rudimentary E820 table that
consists of 2 entries:

  BIOS-e820: [mem 0x0000000000000000-0x0000000000000fff] usable
  BIOS-e820: [mem 0x00000000fffff000-0x00000000ffffffff] reserved

It breaks logic in find_trampoline_placement(): bios_start lands on the
end of the first 4k page and trampoline start gets placed below 0.

Detect underflow and don't touch bios_start for such cases. It makes
kernel ignore E820 table on machines that doesn't have two usable pages
below BIOS_START_MAX.

Fixes: 1b3a62643660 ("x86/boot/compressed/64: Validate trampoline placement against E820")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=203463
Link: https://lkml.kernel.org/r/20190813131654.24378-1-kirill.shutemov@linux.intel.com

Showing 1 changed file with 10 additions and 3 deletions Side-by-side Diff

arch/x86/boot/compressed/pgtable_64.c
Diff comments   View file @ 0a46fff
... ... @@ -72,6 +72,8 @@
72 72  
73 73 /* Find the first usable memory region under bios_start. */
74 74 for (i = boot_params->e820_entries - 1; i >= 0; i--) {
  75 + unsigned long new;
  76 +
75 77 entry = &boot_params->e820_table[i];
76 78  
77 79 /* Skip all entries above bios_start. */
78 80  
79 81  
80 82  
... ... @@ -84,15 +86,20 @@
84 86  
85 87 /* Adjust bios_start to the end of the entry if needed. */
86 88 if (bios_start > entry->addr + entry->size)
87   - bios_start = entry->addr + entry->size;
  89 + new = entry->addr + entry->size;
88 90  
89 91 /* Keep bios_start page-aligned. */
90   - bios_start = round_down(bios_start, PAGE_SIZE);
  92 + new = round_down(new, PAGE_SIZE);
91 93  
92 94 /* Skip the entry if it's too small. */
93   - if (bios_start - TRAMPOLINE_32BIT_SIZE < entry->addr)
  95 + if (new - TRAMPOLINE_32BIT_SIZE < entry->addr)
94 96 continue;
95 97  
  98 + /* Protect against underflow. */
  99 + if (new - TRAMPOLINE_32BIT_SIZE > bios_start)
  100 + break;
  101 +
  102 + bios_start = new;
96 103 break;
97 104 }
98 105