Messages in this thread | | | From | "linfeng (M)" <> | Subject | RE: [PATCH] x86/kaslr: try process e820 entries if can not get suitable regions from efi | Date | Wed, 6 Jan 2021 03:04:04 +0000 |
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> -----Original Message----- > From: Arvind Sankar [mailto:niveditas98@gmail.com] On Behalf Of Arvind > Sankar > Sent: Wednesday, January 6, 2021 5:01 AM > To: Ard Biesheuvel <ardb@kernel.org> > Cc: linfeng (M) <linfeng23@huawei.com>; Arvind Sankar > <nivedita@alum.mit.edu>; Thomas Gleixner <tglx@linutronix.de>; Ingo Molnar > <mingo@redhat.com>; Borislav Petkov <bp@alien8.de>; Huangweidong (C) > <weidong.huang@huawei.com>; Wangjing (Hogan, Cloud Infrastructure > Service Product Dept.) <hogan.wang@huawei.com>; Wangxin (Alexander) > <wangxinxin.wang@huawei.com>; Linux Kernel Mailing List > <linux-kernel@vger.kernel.org>; Eric W. Biederman <ebiederm@xmission.com> > Subject: Re: [PATCH] x86/kaslr: try process e820 entries if can not get suitable > regions from efi > > On Tue, Jan 05, 2021 at 09:54:52AM +0100, Ard Biesheuvel wrote: > > (cc Arvind) > > > > On Tue, 5 Jan 2021 at 09:54, Lin Feng <linfeng23@huawei.com> wrote: > > > > > > On efi64 x86_64 system, the EFI_CONVENTIONAL_MEMORY regions will > not > > > be mapped when making EFI runtime calls. So kexec-tools can not get > > > these from /sys/firmware/efi/runtime-map. Then compressed boot os > > > can not get suitable regions in process_efi_entries and print debug > > > message as follow: > > > Physical KASLR disabled: no suitable memory region! > > > To enable physical kaslr with kexec, call process_e820_entries when > > > no suitable regions in efi memmaps. > > > > > > Signed-off-by: Lin Feng <linfeng23@huawei.com> > > > > > > --- > > > > > > I find a regular of Kernel code and data placement with kexec. It > > > seems unsafe. The reason is showed above. > > > > > > I'm not familiar with efi firmware. I wonder if there are some risks > > > to get regions according to e820 when there is no suitable region in > > > efi memmaps. > > > --- > > > arch/x86/boot/compressed/kaslr.c | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/arch/x86/boot/compressed/kaslr.c > > > b/arch/x86/boot/compressed/kaslr.c > > > index b92fffbe761f..dbd7244b71aa 100644 > > > --- a/arch/x86/boot/compressed/kaslr.c > > > +++ b/arch/x86/boot/compressed/kaslr.c > > > @@ -685,6 +685,7 @@ process_efi_entries(unsigned long minimum, > > > unsigned long image_size) { > > > struct efi_info *e = &boot_params->efi_info; > > > bool efi_mirror_found = false; > > > + bool efi_mem_region_found = false; > > > struct mem_vector region; > > > efi_memory_desc_t *md; > > > unsigned long pmap; > > > @@ -742,12 +743,13 @@ process_efi_entries(unsigned long minimum, > unsigned long image_size) > > > !(md->attribute & > EFI_MEMORY_MORE_RELIABLE)) > > > continue; > > > > > > + efi_mem_region_found = false; > ^^ this should be true, not false. You're right. It should be true here. Thanks for pointing out. > > Other than that, I think this should be okay. The reason EFI memmap is > preferred over E820, according to commit > > 0982adc74673 ("x86/boot/KASLR: Work around firmware bugs by excluding > EFI_BOOT_SERVICES_* and EFI_LOADER_* from KASLR's choice") > > was to avoid allocating inside EFI_BOOT_SERVICES/EFI_LOADER_DATA etc. > That's not a danger during kexec, and I believe runtime services regions should > be marked as reserved in the E820 map, right? Yes. > > Also, something a little fishy-looking here is that the first loop to see if there is > any EFI_MEMORY_MORE_RELIABLE region does not apply any of the checks on > the memory region type/attributes. If there is a mirror region but it isn't > conventional memory, or if it was soft-reserved, we shouldn't be setting > efi_mirror_found. I think so. And I wonder if the memory mirror doesn't work with kexec and ksalr only this patch used, because a lot of efi information is lost and e820 don't have any mirror regions information. Due to resource constraints, I haven't tested it yet. But it seems so. > > > > > region.start = md->phys_addr; > > > region.size = md->num_pages << EFI_PAGE_SHIFT; > > > if (process_mem_region(®ion, minimum, > image_size)) > > > break; > > > } > > > - return true; > > > + return efi_mem_region_found; > > > } > > > #else > > > static inline bool > > > -- > > > 2.23.0 > > >
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