Re: [PATCH v5 28/32] x86/mm, kexec: Allow kexec to be used with SME

From: Xunlei Pang
Date: Wed May 31 2017 - 11:02:57 EST

On 05/31/2017 at 01:46 AM, Tom Lendacky wrote:
> On 5/25/2017 11:17 PM, Xunlei Pang wrote:
>> On 04/19/2017 at 05:21 AM, Tom Lendacky wrote:
>>> Provide support so that kexec can be used to boot a kernel when SME is
>>> enabled.
>>>
>>> Support is needed to allocate pages for kexec without encryption. This
>>> is needed in order to be able to reboot in the kernel in the same manner
>>> as originally booted.
>>
>> Hi Tom,
>>
>> Looks like kdump will break, I didn't see the similar handling for kdump cases, see kernel:
>> kimage_alloc_crash_control_pages(), kimage_load_crash_segment(), etc. >
>> We need to support kdump with SME, kdump kernel/initramfs/purgatory/elfcorehdr/etc
>> are all loaded into the reserved memory(see crashkernel=X) by userspace kexec-tools.
>> I think a straightforward way would be to mark the whole reserved memory range without
>> encryption before loading all the kexec segments for kdump, I guess we can handle this
>> easily in arch_kexec_unprotect_crashkres().
>
> Yes, that would work.
>
>>
>> Moreover, now that "elfcorehdr=X" is left as decrypted, it needs to be remapped to the
>> encrypted data.
>
> This is an area that I'm not familiar with, so I don't completely
> understand the flow in regards to where/when/how the ELF headers are
> copied and what needs to be done.
>
> Can you elaborate a bit on this?

"elfcorehdr" is generated by userspace kexec-tools(git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git), it's
actually ELF CORE header data(elf header, PT_LOAD/PT_NOTE program header), see kexec/crashdump-elf.c::FUNC().

For kdump case, it will be put in some reserved crash memory allocated by kexec-tools, and passed the corresponding
start address of the allocated reserved crash memory to kdump kernel via "elfcorehdr=", please see kernel functions
setup_elfcorehdr() and vmcore_init() for how it is parsed by kdump kernel.

Regards,
Xunlei

>>
>>>
>>> Additionally, when shutting down all of the CPUs we need to be sure to
>>> flush the caches and then halt. This is needed when booting from a state
>>> where SME was not active into a state where SME is active (or vice-versa).
>>> Without these steps, it is possible for cache lines to exist for the same
>>> physical location but tagged both with and without the encryption bit. This
>>> can cause random memory corruption when caches are flushed depending on
>>> which cacheline is written last.
>>>
>>> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
>>> ---
>>> arch/x86/include/asm/init.h | 1 +
>>> arch/x86/include/asm/irqflags.h | 5 +++++
>>> arch/x86/include/asm/kexec.h | 8 ++++++++
>>> arch/x86/include/asm/pgtable_types.h | 1 +
>>> arch/x86/kernel/machine_kexec_64.c | 35 +++++++++++++++++++++++++++++++++-
>>> arch/x86/kernel/process.c | 26 +++++++++++++++++++++++--
>>> arch/x86/mm/ident_map.c | 11 +++++++----
>>> include/linux/kexec.h | 14 ++++++++++++++
>>> kernel/kexec_core.c | 7 +++++++
>>> 9 files changed, 101 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h
>>> index 737da62..b2ec511 100644
>>> --- a/arch/x86/include/asm/init.h
>>> +++ b/arch/x86/include/asm/init.h
>>> @@ -6,6 +6,7 @@ struct x86_mapping_info {
>>> void *context; /* context for alloc_pgt_page */
>>> unsigned long pmd_flag; /* page flag for PMD entry */
>>> unsigned long offset; /* ident mapping offset */
>>> + unsigned long kernpg_flag; /* kernel pagetable flag override */
>>> };
>>> int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
>>> diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
>>> index ac7692d..38b5920 100644
>>> --- a/arch/x86/include/asm/irqflags.h
>>> +++ b/arch/x86/include/asm/irqflags.h
>>> @@ -58,6 +58,11 @@ static inline __cpuidle void native_halt(void)
>>> asm volatile("hlt": : :"memory");
>>> }
>>> +static inline __cpuidle void native_wbinvd_halt(void)
>>> +{
>>> + asm volatile("wbinvd; hlt" : : : "memory");
>>> +}
>>> +
>>> #endif
>>> #ifdef CONFIG_PARAVIRT
>>> diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
>>> index 70ef205..e8183ac 100644
>>> --- a/arch/x86/include/asm/kexec.h
>>> +++ b/arch/x86/include/asm/kexec.h
>>> @@ -207,6 +207,14 @@ struct kexec_entry64_regs {
>>> uint64_t r15;
>>> uint64_t rip;
>>> };
>>> +
>>> +extern int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages,
>>> + gfp_t gfp);
>>> +#define arch_kexec_post_alloc_pages arch_kexec_post_alloc_pages
>>> +
>>> +extern void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages);
>>> +#define arch_kexec_pre_free_pages arch_kexec_pre_free_pages
>>> +
>>> #endif
>>> typedef void crash_vmclear_fn(void);
>>> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
>>> index ce8cb1c..0f326f4 100644
>>> --- a/arch/x86/include/asm/pgtable_types.h
>>> +++ b/arch/x86/include/asm/pgtable_types.h
>>> @@ -213,6 +213,7 @@ enum page_cache_mode {
>>> #define PAGE_KERNEL __pgprot(__PAGE_KERNEL | _PAGE_ENC)
>>> #define PAGE_KERNEL_RO __pgprot(__PAGE_KERNEL_RO | _PAGE_ENC)
>>> #define PAGE_KERNEL_EXEC __pgprot(__PAGE_KERNEL_EXEC | _PAGE_ENC)
>>> +#define PAGE_KERNEL_EXEC_NOENC __pgprot(__PAGE_KERNEL_EXEC)
>>> #define PAGE_KERNEL_RX __pgprot(__PAGE_KERNEL_RX | _PAGE_ENC)
>>> #define PAGE_KERNEL_NOCACHE __pgprot(__PAGE_KERNEL_NOCACHE | _PAGE_ENC)
>>> #define PAGE_KERNEL_LARGE __pgprot(__PAGE_KERNEL_LARGE | _PAGE_ENC)
>>> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
>>> index 085c3b3..11c0ca9 100644
>>> --- a/arch/x86/kernel/machine_kexec_64.c
>>> +++ b/arch/x86/kernel/machine_kexec_64.c
>>> @@ -86,7 +86,7 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
>>> set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
>>> }
>>> pte = pte_offset_kernel(pmd, vaddr);
>>> - set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC));
>>> + set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC_NOENC));
>>> return 0;
>>> err:
>>> free_transition_pgtable(image);
>>> @@ -114,6 +114,7 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
>>> .alloc_pgt_page = alloc_pgt_page,
>>> .context = image,
>>> .pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
>>> + .kernpg_flag = _KERNPG_TABLE_NOENC,
>>> };
>>> unsigned long mstart, mend;
>>> pgd_t *level4p;
>>> @@ -597,3 +598,35 @@ void arch_kexec_unprotect_crashkres(void)
>>> {
>>> kexec_mark_crashkres(false);
>>> }
>>> +
>>> +int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, gfp_t gfp)
>>> +{
>>> + int ret;
>>> +
>>> + if (sme_active()) {
>>> + /*
>>> + * If SME is active we need to be sure that kexec pages are
>>> + * not encrypted because when we boot to the new kernel the
>>> + * pages won't be accessed encrypted (initially).
>>> + */
>>> + ret = set_memory_decrypted((unsigned long)vaddr, pages);
>>> + if (ret)
>>> + return ret;
>>> +
>>> + if (gfp & __GFP_ZERO)
>>> + memset(vaddr, 0, pages * PAGE_SIZE);
>>> + }
>>> +
>>> + return 0;
>>> +}
>>> +
>>> +void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages)
>>> +{
>>> + if (sme_active()) {
>>> + /*
>>> + * If SME is active we need to reset the pages back to being
>>> + * an encrypted mapping before freeing them.
>>> + */
>>> + set_memory_encrypted((unsigned long)vaddr, pages);
>>> + }
>>> +}
>>> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
>>> index 0bb8842..f4e5de6 100644
>>> --- a/arch/x86/kernel/process.c
>>> +++ b/arch/x86/kernel/process.c
>>> @@ -24,6 +24,7 @@
>>> #include <linux/cpuidle.h>
>>> #include <trace/events/power.h>
>>> #include <linux/hw_breakpoint.h>
>>> +#include <linux/kexec.h>
>>> #include <asm/cpu.h>
>>> #include <asm/apic.h>
>>> #include <asm/syscalls.h>
>>> @@ -355,8 +356,25 @@ bool xen_set_default_idle(void)
>>> return ret;
>>> }
>>> #endif
>>> +
>>> void stop_this_cpu(void *dummy)
>>> {
>>> + bool do_wbinvd_halt = false;
>>> +
>>> + if (kexec_in_progress && boot_cpu_has(X86_FEATURE_SME)) {
>>> + /*
>>> + * If we are performing a kexec and the processor supports
>>> + * SME then we need to clear out cache information before
>>> + * halting. With kexec, going from SME inactive to SME active
>>> + * requires clearing cache entries so that addresses without
>>> + * the encryption bit set don't corrupt the same physical
>>> + * address that has the encryption bit set when caches are
>>> + * flushed. Perform a wbinvd followed by a halt to achieve
>>> + * this.
>>> + */
>>> + do_wbinvd_halt = true;
>>> + }
>>> +
>>> local_irq_disable();
>>> /*
>>> * Remove this CPU:
>>> @@ -365,8 +383,12 @@ void stop_this_cpu(void *dummy)
>>> disable_local_APIC();
>>> mcheck_cpu_clear(this_cpu_ptr(&cpu_info));
>>> - for (;;)
>>> - halt();
>>> + for (;;) {
>>> + if (do_wbinvd_halt)
>>> + native_wbinvd_halt();
>>> + else
>>> + halt();
>>> + }
>>> }
>>> /*
>>> diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
>>> index 04210a2..2c9fd3e 100644
>>> --- a/arch/x86/mm/ident_map.c
>>> +++ b/arch/x86/mm/ident_map.c
>>> @@ -20,6 +20,7 @@ static void ident_pmd_init(struct x86_mapping_info *info, pmd_t *pmd_page,
>>> static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page,
>>> unsigned long addr, unsigned long end)
>>> {
>>> + unsigned long kernpg_flag = info->kernpg_flag ? : _KERNPG_TABLE;
>>> unsigned long next;
>>> for (; addr < end; addr = next) {
>>> @@ -39,7 +40,7 @@ static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page,
>>> if (!pmd)
>>> return -ENOMEM;
>>> ident_pmd_init(info, pmd, addr, next);
>>> - set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
>>> + set_pud(pud, __pud(__pa(pmd) | kernpg_flag));
>>> }
>>> return 0;
>>> @@ -48,6 +49,7 @@ static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page,
>>> static int ident_p4d_init(struct x86_mapping_info *info, p4d_t *p4d_page,
>>> unsigned long addr, unsigned long end)
>>> {
>>> + unsigned long kernpg_flag = info->kernpg_flag ? : _KERNPG_TABLE;
>>> unsigned long next;
>>> for (; addr < end; addr = next) {
>>> @@ -67,7 +69,7 @@ static int ident_p4d_init(struct x86_mapping_info *info, p4d_t *p4d_page,
>>> if (!pud)
>>> return -ENOMEM;
>>> ident_pud_init(info, pud, addr, next);
>>> - set_p4d(p4d, __p4d(__pa(pud) | _KERNPG_TABLE));
>>> + set_p4d(p4d, __p4d(__pa(pud) | kernpg_flag));
>>> }
>>> return 0;
>>> @@ -76,6 +78,7 @@ static int ident_p4d_init(struct x86_mapping_info *info, p4d_t *p4d_page,
>>> int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
>>> unsigned long pstart, unsigned long pend)
>>> {
>>> + unsigned long kernpg_flag = info->kernpg_flag ? : _KERNPG_TABLE;
>>> unsigned long addr = pstart + info->offset;
>>> unsigned long end = pend + info->offset;
>>> unsigned long next;
>>> @@ -104,14 +107,14 @@ int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
>>> if (result)
>>> return result;
>>> if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
>>> - set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
>>> + set_pgd(pgd, __pgd(__pa(p4d) | kernpg_flag));
>>> } else {
>>> /*
>>> * With p4d folded, pgd is equal to p4d.
>>> * The pgd entry has to point to the pud page table in this case.
>>> */
>>> pud_t *pud = pud_offset(p4d, 0);
>>> - set_pgd(pgd, __pgd(__pa(pud) | _KERNPG_TABLE));
>>> + set_pgd(pgd, __pgd(__pa(pud) | kernpg_flag));
>>> }
>>> }
>>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>>> index d419d0e..1c76e3b 100644
>>> --- a/include/linux/kexec.h
>>> +++ b/include/linux/kexec.h
>>> @@ -383,6 +383,20 @@ static inline void *boot_phys_to_virt(unsigned long entry)
>>> return phys_to_virt(boot_phys_to_phys(entry));
>>> }
>>> +#ifndef arch_kexec_post_alloc_pages
>>> +static inline int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages,
>>> + gfp_t gfp)
>>> +{
>>> + return 0;
>>> +}
>>> +#endif
>>> +
>>> +#ifndef arch_kexec_pre_free_pages
>>> +static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages)
>>> +{
>>> +}
>>> +#endif
>>> +
>>> #else /* !CONFIG_KEXEC_CORE */
>>> struct pt_regs;
>>> struct task_struct;
>>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>>> index bfe62d5..bb5e7e3 100644
>>> --- a/kernel/kexec_core.c
>>> +++ b/kernel/kexec_core.c
>>> @@ -38,6 +38,7 @@
>>> #include <linux/syscore_ops.h>
>>> #include <linux/compiler.h>
>>> #include <linux/hugetlb.h>
>>> +#include <linux/mem_encrypt.h>
>>> #include <asm/page.h>
>>> #include <asm/sections.h>
>>> @@ -315,6 +316,9 @@ static struct page *kimage_alloc_pages(gfp_t gfp_mask, unsigned int order)
>>> count = 1 << order;
>>> for (i = 0; i < count; i++)
>>> SetPageReserved(pages + i);
>>> +
>>> + arch_kexec_post_alloc_pages(page_address(pages), count,
>>> + gfp_mask);
>>> }
>>> return pages;
>>> @@ -326,6 +330,9 @@ static void kimage_free_pages(struct page *page)
>>> order = page_private(page);
>>> count = 1 << order;
>>> +
>>> + arch_kexec_pre_free_pages(page_address(page), count);
>>> +
>>> for (i = 0; i < count; i++)
>>> ClearPageReserved(page + i);
>>> __free_pages(page, order);
>>>
>>>
>>> _______________________________________________
>>> kexec mailing list
>>> kexec@xxxxxxxxxxxxxxxxxxx
>>> http://lists.infradead.org/mailman/listinfo/kexec
>>