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

[Xunlei Pang <xpang@redhat.com>]

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().

Moreover, now that "elfcorehdr=X" is left as decrypted, it needs to be remapped to the
encrypted data.

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