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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: linux-efi , Linux ARM , Wupeng Ma , Linux Memory Management List References: <20220503152131.263711-1-ardb@kernel.org> <9472d1d5-7f03-eaaf-2846-a4340163d5c0@huawei.com> From: Kefeng Wang In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit 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: rspam02 X-Rspamd-Queue-Id: 1875C800A2 X-Stat-Signature: 36c8tp9xoguns7k6ktmff1pp8goxjwwx X-Rspam-User: Authentication-Results: imf02.hostedemail.com; dkim=none; spf=pass (imf02.hostedemail.com: domain of wangkefeng.wang@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=wangkefeng.wang@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-HE-Tag: 1651801379-409126 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 2022/5/6 0:12, Ard Biesheuvel wrote: > On Thu, 5 May 2022 at 15:43, Kefeng Wang wrote: >> >> 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. >> > Why? I mean, why is 4G a magic number also on arm64? Please ignore this, replied in the previous email. > >> Do we need some fallback mechanism in case of small mirror slots which >> >> leads to fail allocation for Image? >> > This code only counts slots that are large enough to hold the Image so > this can never happen. If total_mirrored_slots > 0, there is at least > one possible placement of the kernel where it falls entirely inside a > EFI_MORE_RELIABLE region. I see,  slots = get_entry_num_slots(md, *size*, ilog2(align)); Thanks. Reviewed-by: Kefeng Wang > >>> /* 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; > .