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Message-ID: <7058b8d8-c0cb-108e-0db9-2fdf5fb154cf@huawei.com>
Date:   Thu, 19 May 2022 19:09:18 +0800
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Subject: Re: [PATCH 0/2] Add support to relocate kernel image to mirrored
 region
To:     <ardb@kernel.org>
CC:     <akpm@linux-foundation.org>, <catalin.marinas@arm.com>,
        <will@kernel.org>, <corbet@lwn.net>, <tglx@linutronix.de>,
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        <platform-driver-x86@vger.kernel.org>, <linux-mm@kvack.org>,
        <mawupeng1@huawei.com>
References: <CAMj1kXGSStDgj9ABmUaTLnBmpQFksh3wx4tx=mJohum4GQe3Gg@mail.gmail.com>
 <20220419070150.254377-1-mawupeng1@huawei.com>
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 <c65d22b4-f654-21aa-bd5f-d4f8b0939a25@huawei.com>
From:   mawupeng <mawupeng1@huawei.com>
In-Reply-To: <c65d22b4-f654-21aa-bd5f-d4f8b0939a25@huawei.com>
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在 2022/5/7 17:28, mawupeng 写道:
> 
> 
> 在 2022/5/3 17:58, Ard Biesheuvel 写道:
>> On Tue, 19 Apr 2022 at 08:43, Wupeng Ma <mawupeng1@huawei.com> wrote:
>>>
>>> From: Ma Wupeng <mawupeng1@huawei.com>
>>>
>>> Now system image will perfer to be located to mirrored regions both KASLR
>>> on and off.
>>>
>>
>> Hello Ma Wupeng,
>>
>> I wonder if we could simplify this as follows:
>> - ignore the non-KASLR case for now, and rely on the bootloader  > load the image into mirrored memory if it exists;
> 
> In grub, memory for static image is allocated via the following path:
> 
> grub_cmd_linux
>    kernel = grub_malloc(filelen)
>    kernel_alloc_addr = grub_efi_allocate_any_pages (kernel_alloc_pages)
>    grub_memcpy (kernel_addr, kernel, grub_min(filelen, kernel_size))
>     grub_loader_set (grub_linux_boot, grub_linux_unload, 0)
> 
> Can we get memory from mirrored region by the following steps:
> 1. get memory map by calling grub_efi_get_memory_map()
> 2. iter all memory map to find a suitable mirrored memory area
> 3. locate kernel image to this area
> 
> So, if kaslr is not enabled
>   - grub will load kernel into mirrored region
> else
>   - arm64-stub.c will relocate kernel image to mirrored region
> 
> Is this feasible?

Is this a feasible proposal to relocate the static kernel image itself
into more reliable memory?

> 
>> - simplify the KASLR case to the below.
> 
> Yes, we can certainly do this. I will remove my code and use yours.
> 
>>
>> I think this is reasonable, because it means we take mirrored memory
>> into account when we decide to move the image anyway, but expect the
>> boot chain to take care of this if there is no need to move the image.
>>
>> -------------8<------------------
>> --- a/drivers/firmware/efi/libstub/randomalloc.c
>> +++ b/drivers/firmware/efi/libstub/randomalloc.c
>> @@ -56,6 +56,7 @@ efi_status_t efi_random_alloc(unsigned long size,
>>                                unsigned long random_seed)
>>   {
>>          unsigned long map_size, desc_size, total_slots = 0, target_slot;
>> +       unsigned long total_mirrored_slots = 0;
>>          unsigned long buff_size;
>>          efi_status_t status;
>>          efi_memory_desc_t *memory_map;
>> @@ -86,8 +87,14 @@ efi_status_t efi_random_alloc(unsigned long size,
>>                  slots = get_entry_num_slots(md, size, ilog2(align));
>>                  MD_NUM_SLOTS(md) = slots;
>>                  total_slots += slots;
>> +               if (md->attribute & EFI_MEMORY_MORE_RELIABLE)
>> +                       total_mirrored_slots += slots;
>>          }
>>
>> +       /* only consider mirrored slots for randomization if any exist */
>> +       if (total_mirrored_slots > 0)
>> +               total_slots = total_mirrored_slots;
>> +
>>          /* find a random number between 0 and total_slots */
>>          target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
>>
>> @@ -107,6 +114,10 @@ efi_status_t efi_random_alloc(unsigned long size,
>>                  efi_physical_addr_t target;
>>                  unsigned long pages;
>>
>> +               if (total_mirrored_slots > 0 &&
>> +                   !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
>> +                       continue;
>> +
>>                  if (target_slot >= MD_NUM_SLOTS(md)) {
>>                          target_slot -= MD_NUM_SLOTS(md);
>>                          continue;
>> .