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

Tom Lendacky
2017-05-30T17:46:42Z

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?

Thanks,
Tom

>
> 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);
>>
>>
>> _______________________________________________
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