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SubjectRe: [PATCH v5 4/4] x86/mm/KASLR: Adjust the padding size for the direct mapping.
On 11/15/19 at 09:49am, Masayoshi Mizuma wrote:
> From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
>
> The system sometimes crashes while memory hot-adding on KASLR
> enabled system. The crash happens because the regions pointed by
> kaslr_regions[].base are overwritten by the hot-added memory.
>
> It happens because of the padding size for kaslr_regions[].base isn't
> enough for the system whose physical memory layout has huge space for
> memory hotplug. kaslr_regions[].base points "actual installed
> memory size + padding" or higher address. So, if the "actual + padding"
> is lower address than the maximum memory address, which means the memory
> address reachable by memory hot-add, kaslr_regions[].base is destroyed by
> the overwritten.
>
> address
> ^
> |------- maximum memory address (Hotplug)
> | ^
> |------- kaslr_regions[0].base | Hotadd-able region
> | ^ |
> | | padding |
> | V V
> |------- actual memory address (Installed on boot)
> |
>
> Fix it by getting the maximum memory address from SRAT and store
> the value in boot_param, then set the padding size while KASLR
> initializing if the default padding size isn't enough.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
> ---
> arch/x86/mm/kaslr.c | 57 +++++++++++++++++++++++++++++++++------------
> 1 file changed, 42 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> index dc6182eecefa..1f0aa9e68226 100644
> --- a/arch/x86/mm/kaslr.c
> +++ b/arch/x86/mm/kaslr.c
> @@ -70,15 +70,52 @@ static inline bool kaslr_memory_enabled(void)
> return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
> }
>
> +/*
> + * Even though a huge virtual address space is reserved for the direct
> + * mapping of physical memory, e.g in 4-level paging mode, it's 64TB,
> + * rare system can own enough physical memory to use it up, most are
> + * even less than 1TB. So with KASLR enabled, we adapt the size of
> + * direct mapping area to the size of actual physical memory plus the
> + * configured padding CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING.
> + * The left part will be taken out to join memory randomization.

The doc doesn't reflect the the case of boot_params.max_addr existed?

Otherwise, it looks good to me and easy to understand. You can remove my
'Signed-off' and feel free to add my ack.

Acked-by: Baoquan He <bhe@redhat.com>

Thanks
Baoquan

> + */
> +static inline unsigned long calc_direct_mapping_size(void)
> +{
> + unsigned long size_tb, memory_tb;
> +
> + memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
> + CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
> +
> +#ifdef CONFIG_MEMORY_HOTPLUG
> + if (boot_params.max_addr) {
> + unsigned long maximum_tb;
> +
> + maximum_tb = DIV_ROUND_UP(boot_params.max_addr,
> + 1UL << TB_SHIFT);
> +
> + if (maximum_tb > memory_tb)
> + memory_tb = maximum_tb;
> + }
> +#endif
> + size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);
> +
> + /*
> + * Adapt physical memory region size based on available memory
> + */
> + if (memory_tb < size_tb)
> + size_tb = memory_tb;
> +
> + return size_tb;
> +}
> +
> /* Initialize base and padding for each memory region randomized with KASLR */
> void __init kernel_randomize_memory(void)
> {
> - size_t i;
> - unsigned long vaddr_start, vaddr;
> - unsigned long rand, memory_tb;
> - struct rnd_state rand_state;
> + unsigned long vaddr_start, vaddr, rand;
> unsigned long remain_entropy;
> unsigned long vmemmap_size;
> + struct rnd_state rand_state;
> + size_t i;
>
> vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4;
> vaddr = vaddr_start;
> @@ -95,20 +132,10 @@ void __init kernel_randomize_memory(void)
> if (!kaslr_memory_enabled())
> return;
>
> - kaslr_regions[0].size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);
> + kaslr_regions[0].size_tb = calc_direct_mapping_size();
> kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;
>
> - /*
> - * Update Physical memory mapping to available and
> - * add padding if needed (especially for memory hotplug support).
> - */
> BUG_ON(kaslr_regions[0].base != &page_offset_base);
> - memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
> - CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
> -
> - /* Adapt phyiscal memory region size based on available memory */
> - if (memory_tb < kaslr_regions[0].size_tb)
> - kaslr_regions[0].size_tb = memory_tb;
>
> /*
> * Calculate the vmemmap region size in TBs, aligned to a TB
> --
> 2.20.1
>

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