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

[Xunlei Pang <xpang@redhat.com>]

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@amd.com>
>>> ---
>>>   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@lists.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/kexec
>>

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