[ Upstream commit 0a46fff2f9108c2c44218380a43a736cf4612541 ]
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... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/boot/compressed/pgtable_64.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c index f8debf7aeb4c1..f0537a1f7fc25 100644 --- a/arch/x86/boot/compressed/pgtable_64.c +++ b/arch/x86/boot/compressed/pgtable_64.c @@ -73,6 +73,8 @@ static unsigned long find_trampoline_placement(void)
/* Find the first usable memory region under bios_start. */ for (i = boot_params->e820_entries - 1; i >= 0; i--) { + unsigned long new; + entry = &boot_params->e820_table[i];
/* Skip all entries above bios_start. */ @@ -85,15 +87,20 @@ static unsigned long find_trampoline_placement(void)
/* Adjust bios_start to the end of the entry if needed. */ if (bios_start > entry->addr + entry->size) - bios_start = entry->addr + entry->size; + new = entry->addr + entry->size;
/* Keep bios_start page-aligned. */ - bios_start = round_down(bios_start, PAGE_SIZE); + new = round_down(new, PAGE_SIZE);
/* Skip the entry if it's too small. */ - if (bios_start - TRAMPOLINE_32BIT_SIZE < entry->addr) + if (new - TRAMPOLINE_32BIT_SIZE < entry->addr) continue;
+ /* Protect against underflow. */ + if (new - TRAMPOLINE_32BIT_SIZE > bios_start) + break; + + bios_start = new; break; }