Date: Thu, 15 Dec 2016 11:45:10 -0800 From: Thomas Garnier <thgarnie@...gle.com> To: "Eric W. Biederman" <ebiederm@...ssion.com> Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Andrew Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>, Xunlei Pang <xlpang@...hat.com>, HATAYAMA Daisuke <d.hatayama@...fujitsu.com>, "the arch/x86 maintainers" <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, kexec@...ts.infradead.org, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH] Revert "Revert "kdump, vmcoreinfo: report memory sections virtual addresses"" On Thu, Dec 15, 2016 at 10:16 AM, Thomas Garnier <thgarnie@...gle.com> wrote: > On Thu, Dec 15, 2016 at 9:50 AM, Eric W. Biederman > <ebiederm@...ssion.com> wrote: >> Thomas Garnier <thgarnie@...gle.com> writes: >> >>> This reverts commit 49fd897573c97b0eaf10f47d850027d78c456cd7. >>> >>> Reverting back to commit 0549a3c because the values are used by crash >>> and other tools already. I expected this commit would not go through given >>> the unresolved comments. I want it to be easy to resolve major memory >>> section positions when KASLR memory randomization is enabled. >> >> This patch is broken. The commit referenced is wrong, > > Yes, I based them on linux-next. I can update them to linux main tree. > Sorry about that. > >> as is the justification. >> >> These values are not in fact widely used by userspace (they are brand new). >> > > They were new and got through to the master tree before and on 4.9. I > didn't get any feedback on that when it went through. > >> This is a very fragile approach relying on kernel implementation >> details, so if we can do anything else that is more robust it >> is much more likely to pass the test of time. >> >> And yes a more robust implementation has been already discussed. >> > > There were discussed for the PAGE_OFFSET but not VMALLOC_START. What's > your approach for it? > Also with improvement on KASLR memory randomization, I don't think we should assume memory sections by looking at PT_LOAD first entries. We will certainly try to randomize the order. That's why I thought clearly indicating which VA define which memory section was a good idea. I also want to find a time proof approach where we can use it no matter the changes to KASLR. >> Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com> >> >>> >>> Signed-off-by: Thomas Garnier <thgarnie@...gle.com> >>> --- >>> arch/x86/kernel/machine_kexec_64.c | 3 +++ >>> include/linux/kexec.h | 6 ++++++ >>> 2 files changed, 9 insertions(+) >>> >>> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c >>> index 2e3c34b..05f3367 100644 >>> --- a/arch/x86/kernel/machine_kexec_64.c >>> +++ b/arch/x86/kernel/machine_kexec_64.c >>> @@ -339,6 +339,9 @@ void arch_crash_save_vmcoreinfo(void) >>> kaslr_offset()); >>> VMCOREINFO_NUMBER(KERNEL_IMAGE_SIZE); >>> VMCOREINFO_PHYS_BASE(phys_base); >>> + VMCOREINFO_PAGE_OFFSET(PAGE_OFFSET); >>> + VMCOREINFO_VMALLOC_START(VMALLOC_START); >>> + VMCOREINFO_VMEMMAP_START(VMEMMAP_START); >>> } >>> >>> /* arch-dependent functionality related to kexec file-based syscall */ >>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h >>> index e98e546..ff9c876 100644 >>> --- a/include/linux/kexec.h >>> +++ b/include/linux/kexec.h >>> @@ -285,6 +285,12 @@ phys_addr_t paddr_vmcoreinfo_note(void); >>> vmcoreinfo_append_str("CONFIG_%s=y\n", #name) >>> #define VMCOREINFO_PHYS_BASE(value) \ >>> vmcoreinfo_append_str("PHYS_BASE=%lx\n", (unsigned long)value) >>> +#define VMCOREINFO_PAGE_OFFSET(value) \ >>> + vmcoreinfo_append_str("PAGE_OFFSET=%lx\n", (unsigned long)value) >>> +#define VMCOREINFO_VMALLOC_START(value) \ >>> + vmcoreinfo_append_str("VMALLOC_START=%lx\n", (unsigned long)value) >>> +#define VMCOREINFO_VMEMMAP_START(value) \ >>> + vmcoreinfo_append_str("VMEMMAP_START=%lx\n", (unsigned long)value) >>> >>> extern struct kimage *kexec_image; >>> extern struct kimage *kexec_crash_image; > > > > -- > Thomas -- Thomas
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