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SubjectRe: [PATCH v6 30/34] x86/mm, kexec: Allow kexec to be used with SME
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On 6/15/2017 5:03 AM, Borislav Petkov wrote:
> On Wed, Jun 07, 2017 at 02:18:27PM -0500, 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.
>>
>> 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/kexec.h | 8 ++++++++
>> arch/x86/include/asm/pgtable_types.h | 1 +
>> arch/x86/kernel/machine_kexec_64.c | 35 +++++++++++++++++++++++++++++++++-
>> arch/x86/kernel/process.c | 17 +++++++++++++++--
>> arch/x86/mm/ident_map.c | 12 ++++++++----
>> include/linux/kexec.h | 14 ++++++++++++++
>> kernel/kexec_core.c | 6 ++++++
>> 8 files changed, 87 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h
>> index 474eb8c..05c4aa0 100644
>> --- a/arch/x86/include/asm/init.h
>> +++ b/arch/x86/include/asm/init.h
>> @@ -7,6 +7,7 @@ struct x86_mapping_info {
>> unsigned long page_flag; /* page flag for PMD or PUD entry */
>> unsigned long offset; /* ident mapping offset */
>> bool direct_gbpages; /* PUD level 1GB page support */
>> + 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/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 6f5ca4e..35e069a 100644
>> --- a/arch/x86/kernel/machine_kexec_64.c
>> +++ b/arch/x86/kernel/machine_kexec_64.c
>> @@ -87,7 +87,7 @@ 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);
>> @@ -115,6 +115,7 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
>> .alloc_pgt_page = alloc_pgt_page,
>> .context = image,
>> .page_flag = __PAGE_KERNEL_LARGE_EXEC,
>> + .kernpg_flag = _KERNPG_TABLE_NOENC,
>> };
>> unsigned long mstart, mend;
>> pgd_t *level4p;
>> @@ -602,3 +603,35 @@ 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()) {
>
> What happened to flipping the logic and saving an indentation level here?
>
>> + /*
>> + * 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);
>> + }
>
> This is still zeroing the memory a second time. That function has missed
> all my comments from last time.

Hmmm... not sure what happened, I thought I made changes here. I'll
take care of it.

Thanks,
Tom

>

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