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Biederman" Subject: Re: [PATCH] x86/kaslr: try process e820 entries if can not get suitable regions from efi Message-ID: References: <20210105085346.995-1-linfeng23@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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 > > > > --- > > > > 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. 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? 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. > > 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 > >