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Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.5.1 Subject: Re: [PATCH] efi: stub: prefer mirrored memory for randomized allocations Content-Language: en-US To: Ard Biesheuvel , CC: , , References: <20220503152131.263711-1-ardb@kernel.org> From: Kefeng Wang In-Reply-To: <20220503152131.263711-1-ardb@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 540BAA0093 Authentication-Results: imf25.hostedemail.com; dkim=none; spf=pass (imf25.hostedemail.com: domain of wangkefeng.wang@huawei.com designates 45.249.212.255 as permitted sender) smtp.mailfrom=wangkefeng.wang@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Rspam-User: X-Stat-Signature: gf8hutznrg41noooc3mzmykpuauj8y9e X-HE-Tag: 1651758198-690524 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2022/5/3 23:21, Ard Biesheuvel wrote: > If the system exposes memory regions with the EFI_MORE_RELIABLE > attribute, it is implied that it is intended to be used for allocations > that are relatively important, such as the kernel's static image. > > Since efi_random_alloc() is mostly (only) used for allocating space for > the kernel image, let's update it to take this into account, and > disregard all memory without the EFI_MORE_RELIABLE attribute if there is > sufficient memory available that does have this attribute. > > Note that this change only affects booting with randomization enabled. > In other cases, the EFI stub runs the kernel image in place unless its > placement is unsuitable for some reason (i.e., misaligned, or its BSS > overlaps with another allocation), and it is left to the bootloader to > ensure that the kernel was loaded into EFI_MORE_RELIABLE memory if this > is desired. > > Signed-off-by: Ard Biesheuvel > --- > drivers/firmware/efi/libstub/randomalloc.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/drivers/firmware/efi/libstub/randomalloc.c b/drivers/firmware/efi/libstub/randomalloc.c > index 724155b9e10d..07a762910312 100644 > --- 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; > + The kernel will check 4G lower limit to enable kernelcore=mirror feature. Do we need some fallback mechanism in case of small mirror slots which leads to fail allocation for Image? > /* 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;