Re: [PATCH v3 1/1] arm64: mm: correct the inside linear map range during hotplug check
From: Anshuman Khandual
Date: Wed Feb 24 2021 - 02:13:26 EST
On 2/16/21 8:33 PM, Pavel Tatashin wrote:
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Memory hotplug may fail on systems with CONFIG_RANDOMIZE_BASE because the
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linear map range is not checked correctly.
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The start physical address that linear map covers can be actually at the
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end of the range because of randomization. Check that and if so reduce it
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to 0.
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This can be verified on QEMU with setting kaslr-seed to ~0ul:
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memstart_offset_seed = 0xffff
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START: __pa(_PAGE_OFFSET(vabits_actual)) = ffff9000c0000000
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END: __pa(PAGE_END - 1) = 1000bfffffff
This would have tripped the check in mhp_get_pluggable_range()
with errors something like here, which is expected.
Hotplug memory [0x680000000-0x688000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x6c0000000-0x6c8000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x700000000-0x708000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x780000000-0x788000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x7c0000000-0x7c8000000] exceeds maximum addressable range [0x0-0x0]
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Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
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Fixes: 58284a901b42 ("arm64/mm: Validate hotplug range before creating linear mapping")
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Tested-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx>
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---
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arch/arm64/mm/mmu.c | 21 +++++++++++++++++++--
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1 file changed, 19 insertions(+), 2 deletions(-)
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diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
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index ef7698c4e2f0..0d9c115e427f 100644
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--- a/arch/arm64/mm/mmu.c
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+++ b/arch/arm64/mm/mmu.c
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@@ -1447,6 +1447,22 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size)
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struct range arch_get_mappable_range(void)
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{
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struct range mhp_range;
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+ u64 start_linear_pa = __pa(_PAGE_OFFSET(vabits_actual));
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+ u64 end_linear_pa = __pa(PAGE_END - 1);
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+
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+ if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
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+ /*
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+ * Check for a wrap, it is possible because of randomized linear
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+ * mapping the start physical address is actually bigger than
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+ * the end physical address. In this case set start to zero
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+ * because [0, end_linear_pa] range must still be able to cover
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+ * all addressable physical addresses.
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+ */
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+ if (start_linear_pa > end_linear_pa)
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+ start_linear_pa = 0;
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+ }
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+
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+ WARN_ON(start_linear_pa > end_linear_pa);
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/*
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* Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)]
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@@ -1454,8 +1470,9 @@ struct range arch_get_mappable_range(void)
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* range which can be mapped inside this linear mapping range, must
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* also be derived from its end points.
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*/
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- mhp_range.start = __pa(_PAGE_OFFSET(vabits_actual));
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- mhp_range.end = __pa(PAGE_END - 1);
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+ mhp_range.start = start_linear_pa;
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+ mhp_range.end = end_linear_pa;
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+
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return mhp_range;
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}
LGTM.
Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>