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

Xunlei Pang
2017-05-26T04:16:34Z

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);
>
>
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