Re: [PATCH Part1 RFC v3 11/22] x86/sev: Add helper for validating pages in early enc attribute changes

Brijesh Singh
2021-06-14T12:45:21Z

On 6/10/21 10:50 AM, Borislav Petkov wrote:
> On Wed, Jun 02, 2021 at 09:04:05AM -0500, Brijesh Singh wrote:
>> @@ -65,6 +65,12 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
>> /* RMP page size */
>> #define RMP_PG_SIZE_4K 0
>>
>> +/* Memory opertion for snp_prep_memory() */
>> +enum snp_mem_op {
>> + MEMORY_PRIVATE,
>> + MEMORY_SHARED
> See below.
>
>> +};
>> +
>> #ifdef CONFIG_AMD_MEM_ENCRYPT
>> extern struct static_key_false sev_es_enable_key;
>> extern void __sev_es_ist_enter(struct pt_regs *regs);
>> @@ -103,6 +109,11 @@ static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate)
>>
>> return rc;
>> }
>> +void __init early_snp_set_memory_private(unsigned long vaddr, unsigned long paddr,
>> + unsigned int npages);
>> +void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr,
>> + unsigned int npages);
> Align arguments on the opening brace.

Noted.

>
>> +void __init snp_prep_memory(unsigned long paddr, unsigned int sz, int op);
>> #else
>> static inline void sev_es_ist_enter(struct pt_regs *regs) { }
>> static inline void sev_es_ist_exit(void) { }
>> @@ -110,6 +121,15 @@ static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) { ret
>> static inline void sev_es_nmi_complete(void) { }
>> static inline int sev_es_efi_map_ghcbs(pgd_t *pgd) { return 0; }
>> static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate) { return 0; }
>> +static inline void __init
>> +early_snp_set_memory_private(unsigned long vaddr, unsigned long paddr, unsigned int npages)
> Put those { } at the end of the line:
>
> early_snp_set_memory_private(unsigned long vaddr, unsigned long paddr, unsigned int npages) { }
>
> no need for separate lines. Ditto below.

Noted.

>
>> +{
>> +}
>> +static inline void __init
>> +early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr, unsigned int npages)
>> +{
>> +}
>> +static inline void __init snp_prep_memory(unsigned long paddr, unsigned int sz, int op) { }
>> #endif
>>
>> #endif
>> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
>> index 455c09a9b2c2..6e9b45bb38ab 100644
>> --- a/arch/x86/kernel/sev.c
>> +++ b/arch/x86/kernel/sev.c
>> @@ -532,6 +532,111 @@ static u64 get_jump_table_addr(void)
>> return ret;
>> }
>>
>> +static void pvalidate_pages(unsigned long vaddr, unsigned int npages, bool validate)
>> +{
>> + unsigned long vaddr_end;
>> + int rc;
>> +
>> + vaddr = vaddr & PAGE_MASK;
>> + vaddr_end = vaddr + (npages << PAGE_SHIFT);
>> +
>> + while (vaddr < vaddr_end) {
>> + rc = pvalidate(vaddr, RMP_PG_SIZE_4K, validate);
>> + if (WARN(rc, "Failed to validate address 0x%lx ret %d", vaddr, rc))
>> + sev_es_terminate(1, GHCB_TERM_PVALIDATE);
> ^^
>
> I guess that 1 should be a define too, if we have to be correct:
>
> sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PVALIDATE);
>
> or so. Ditto for all other calls of this.

Sure, I will define a macro for it.

>
>> +
>> + vaddr = vaddr + PAGE_SIZE;
>> + }
>> +}
>> +
>> +static void __init early_set_page_state(unsigned long paddr, unsigned int npages, int op)
>> +{
>> + unsigned long paddr_end;
>> + u64 val;
>> +
>> + paddr = paddr & PAGE_MASK;
>> + paddr_end = paddr + (npages << PAGE_SHIFT);
>> +
>> + while (paddr < paddr_end) {
>> + /*
>> + * Use the MSR protocol because this function can be called before the GHCB
>> + * is established.
>> + */
>> + sev_es_wr_ghcb_msr(GHCB_MSR_PSC_REQ_GFN(paddr >> PAGE_SHIFT, op));
>> + VMGEXIT();
>> +
>> + val = sev_es_rd_ghcb_msr();
>> +
>> + if (GHCB_RESP_CODE(val) != GHCB_MSR_PSC_RESP)
> From a previous review:
>
> Does that one need a warning too or am I being too paranoid?

IMO, there is no need to add a warning. This case should happen if its
either a hypervisor bug or hypervisor does not follow the GHCB
specification. I followed the SEV-ES vmgexit handling  and it does not
warn if the hypervisor returns a wrong response code. We simply
terminate the guest.

>
>> + goto e_term;
>> +
>> + if (WARN(GHCB_MSR_PSC_RESP_VAL(val),
>> + "Failed to change page state to '%s' paddr 0x%lx error 0x%llx\n",
>> + op == SNP_PAGE_STATE_PRIVATE ? "private" : "shared",
>> + paddr, GHCB_MSR_PSC_RESP_VAL(val)))
>> + goto e_term;
>> +
>> + paddr = paddr + PAGE_SIZE;
>> + }
>> +
>> + return;
>> +
>> +e_term:
>> + sev_es_terminate(1, GHCB_TERM_PSC);
>> +}
>> +
>> +void __init early_snp_set_memory_private(unsigned long vaddr, unsigned long paddr,
>> + unsigned int npages)
>> +{
>> + if (!sev_feature_enabled(SEV_SNP))
>> + return;
>> +
>> + /* Ask hypervisor to add the memory pages in RMP table as a 'private'. */
> Ask the hypervisor to mark the memory pages as private in the RMP table.

Noted.

>
>> + early_set_page_state(paddr, npages, SNP_PAGE_STATE_PRIVATE);
>> +
>> + /* Validate the memory pages after they've been added in the RMP table. */
>> + pvalidate_pages(vaddr, npages, 1);
>> +}
>> +
>> +void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr,
>> + unsigned int npages)
>> +{
>> + if (!sev_feature_enabled(SEV_SNP))
>> + return;
>> +
>> + /*
>> + * Invalidate the memory pages before they are marked shared in the
>> + * RMP table.
>> + */
>> + pvalidate_pages(vaddr, npages, 0);
>> +
>> + /* Ask hypervisor to make the memory pages shared in the RMP table. */
> mark

Noted.

>> + early_set_page_state(paddr, npages, SNP_PAGE_STATE_SHARED);
>> +}
>> +
>> +void __init snp_prep_memory(unsigned long paddr, unsigned int sz, int op)
>> +{
>> + unsigned long vaddr, npages;
>> +
>> + vaddr = (unsigned long)__va(paddr);
>> + npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
>> +
>> + switch (op) {
>> + case MEMORY_PRIVATE: {
>> + early_snp_set_memory_private(vaddr, paddr, npages);
>> + return;
>> + }
>> + case MEMORY_SHARED: {
>> + early_snp_set_memory_shared(vaddr, paddr, npages);
>> + return;
>> + }
>> + default:
>> + break;
>> + }
>> +
>> + WARN(1, "invalid memory op %d\n", op);
> A lot easier, diff ontop of your patch:

thanks. I will apply it.

I did thought about reusing the VMGEXIT defined macro
SNP_PAGE_STATE_{PRIVATE, SHARED} but I was not sure if you will be okay
with that. Additionally now both the function name and macro name will
include the "SNP". The call will look like this:

snp_prep_memory(paddr, SNP_PAGE_STATE_PRIVATE)

>
> ---
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 7c2cb5300e43..2ad4b5ab3f6c 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -65,12 +65,6 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
> /* RMP page size */
> #define RMP_PG_SIZE_4K 0
>
> -/* Memory opertion for snp_prep_memory() */
> -enum snp_mem_op {
> - MEMORY_PRIVATE,
> - MEMORY_SHARED
> -};
> -
> #ifdef CONFIG_AMD_MEM_ENCRYPT
> extern struct static_key_false sev_es_enable_key;
> extern void __sev_es_ist_enter(struct pt_regs *regs);
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 2a5dce42af35..991d7964cee9 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -662,20 +662,13 @@ void __init snp_prep_memory(unsigned long paddr, unsigned int sz, int op)
> vaddr = (unsigned long)__va(paddr);
> npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
>
> - switch (op) {
> - case MEMORY_PRIVATE: {
> + if (op == SNP_PAGE_STATE_PRIVATE)
> early_snp_set_memory_private(vaddr, paddr, npages);
> - return;
> - }
> - case MEMORY_SHARED: {
> + else if (op == SNP_PAGE_STATE_SHARED)
> early_snp_set_memory_shared(vaddr, paddr, npages);
> - return;
> + else {
> + WARN(1, "invalid memory page op %d\n", op);
> }
> - default:
> - break;
> - }
> -
> - WARN(1, "invalid memory op %d\n", op);
> }
>
> int sev_es_setup_ap_jump_table(struct real_mode_header *rmh)
> ---
>
>> static char sme_early_buffer[PAGE_SIZE] __initdata __aligned(PAGE_SIZE);
>>
>> +/*
>> + * When SNP is active, changes the page state from private to shared before
> s/changes/change/

Noted.

>
>> + * copying the data from the source to destination and restore after the copy.
>> + * This is required because the source address is mapped as decrypted by the
>> + * caller of the routine.
>> + */
>> +static inline void __init snp_memcpy(void *dst, void *src, size_t sz,
>> + unsigned long paddr, bool decrypt)
>> +{
>> + unsigned long npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
>> +
>> + if (!sev_feature_enabled(SEV_SNP) || !decrypt) {
>> + memcpy(dst, src, sz);
>> + return;
>> + }
>> +
>> + /*
>> + * If the paddr needs to be accessed decrypted, mark the page
> What do you mean "If" - this is the SNP version of memcpy. Just say:
>
> /*
> * With SNP, the page address needs to be ...
> */
>
>> + * shared in the RMP table before copying it.
>> + */
>> + early_snp_set_memory_shared((unsigned long)__va(paddr), paddr, npages);
>> +
>> + memcpy(dst, src, sz);
>> +
>> + /* Restore the page state after the memcpy. */
>> + early_snp_set_memory_private((unsigned long)__va(paddr), paddr, npages);
>> +}
>> +
>> /*
>> * This routine does not change the underlying encryption setting of the
>> * page(s) that map this memory. It assumes that eventually the memory is
>> @@ -96,8 +125,8 @@ static void __init __sme_early_enc_dec(resource_size_t paddr,
>> * Use a temporary buffer, of cache-line multiple size, to
>> * avoid data corruption as documented in the APM.
>> */
>> - memcpy(sme_early_buffer, src, len);
>> - memcpy(dst, sme_early_buffer, len);
>> + snp_memcpy(sme_early_buffer, src, len, paddr, enc);
>> + snp_memcpy(dst, sme_early_buffer, len, paddr, !enc);
>>
>> early_memunmap(dst, len);
>> early_memunmap(src, len);
>> @@ -277,9 +306,23 @@ static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
>> else
>> sme_early_decrypt(pa, size);
>>
>> + /*
>> + * If page is getting mapped decrypted in the page table, then the page state
>> + * change in the RMP table must happen before the page table updates.
>> + */
>> + if (!enc)
>> + early_snp_set_memory_shared((unsigned long)__va(pa), pa, 1);
> Merge the two branches:

Noted.

>
> /* Encrypt/decrypt the contents in-place */
> if (enc) {
> sme_early_encrypt(pa, size);
> } else {
> sme_early_decrypt(pa, size);
>
> /*
> * On SNP, the page state change in the RMP table must happen
> * before the page table updates.
> */
> early_snp_set_memory_shared((unsigned long)__va(pa), pa, 1);
> }

- Brijesh