| Message ID | 20211210154332.11526-33-brijesh.singh@amd.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Add AMD Secure Nested Paging (SEV-SNP) Guest Support | expand |
On Fri, Dec 10, 2021 at 09:43:24AM -0600, Brijesh Singh wrote: > Subject: Re: [PATCH v8 32/40] x86/compressed: use firmware-validated CPUID for SEV-SNP guests ^ leafs or so. > From: Michael Roth <michael.roth@amd.com> > > SEV-SNP guests will be provided the location of special 'secrets' > 'CPUID' pages via the Confidential Computing blob. This blob is > provided to the boot kernel either through an EFI config table entry, > or via a setup_data structure as defined by the Linux Boot Protocol. > > Locate the Confidential Computing from these sources and, if found, > use the provided CPUID page/table address to create a copy that the > boot kernel will use when servicing cpuid instructions via a #VC CPUID > handler. > > Signed-off-by: Michael Roth <michael.roth@amd.com> > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com> > --- > arch/x86/boot/compressed/sev.c | 13 ++++++++++ > arch/x86/include/asm/sev.h | 1 + > arch/x86/kernel/sev-shared.c | 43 ++++++++++++++++++++++++++++++++++ > 3 files changed, 57 insertions(+) > > diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c > index 93e125da12cf..29dfb34b5907 100644 > --- a/arch/x86/boot/compressed/sev.c > +++ b/arch/x86/boot/compressed/sev.c > @@ -415,6 +415,19 @@ bool snp_init(struct boot_params *bp) > if (!cc_info) > return false; > > + /* > + * If SEV-SNP-specific Confidential Computing blob is present, then ^ a > + * firmware/bootloader have indicated SEV-SNP support. Verifying this > + * involves CPUID checks which will be more reliable if the SEV-SNP > + * CPUID table is used. See comments for snp_cpuid_info_create() for s/for/over/ ? > + * more details. > + */ > + snp_cpuid_info_create(cc_info); > + > + /* SEV-SNP CPUID table should be set up now. */ > + if (!snp_cpuid_active()) > + sev_es_terminate(1, GHCB_TERM_CPUID); Right, that is not needed now. > * Pass run-time kernel a pointer to CC info via boot_params so EFI > * config table doesn't need to be searched again during early startup > diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h > index cd189c20bcc4..4fa7ca20d7c9 100644 > --- a/arch/x86/include/asm/sev.h > +++ b/arch/x86/include/asm/sev.h > @@ -157,6 +157,7 @@ bool snp_init(struct boot_params *bp); > * sev-shared.c via #include and these declarations can be dropped. > */ > struct cc_blob_sev_info *snp_find_cc_blob_setup_data(struct boot_params *bp); > +void snp_cpuid_info_create(const struct cc_blob_sev_info *cc_info); > #else > static inline void sev_es_ist_enter(struct pt_regs *regs) { } > static inline void sev_es_ist_exit(void) { } > diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c > index bd58a4ce29c8..5cb8f87df4b3 100644 > --- a/arch/x86/kernel/sev-shared.c > +++ b/arch/x86/kernel/sev-shared.c > @@ -403,6 +403,23 @@ snp_cpuid_find_validated_func(u32 func, u32 subfunc, u32 *eax, u32 *ebx, > return false; > } > > +static void __init snp_cpuid_set_ranges(void) > +{ > + const struct snp_cpuid_info *cpuid_info = snp_cpuid_info_get_ptr(); > + int i; > + > + for (i = 0; i < cpuid_info->count; i++) { > + const struct snp_cpuid_fn *fn = &cpuid_info->fn[i]; > + > + if (fn->eax_in == 0x0) > + cpuid_std_range_max = fn->eax; > + else if (fn->eax_in == 0x40000000) > + cpuid_hyp_range_max = fn->eax; > + else if (fn->eax_in == 0x80000000) > + cpuid_ext_range_max = fn->eax; > + } > +} Kinda arbitrary to have a separate function which has a single caller. You can just as well move the loop into snp_cpuid_info_create() and put a comment above it: /* Set CPUID ranges. */ for (i = 0; i < cpuid_info->count; i++) { ... Also, snp_cpuid_info_create() should be called snp_setup_cpuid_table() which is what this thing does. Thx.
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c index 93e125da12cf..29dfb34b5907 100644 --- a/arch/x86/boot/compressed/sev.c +++ b/arch/x86/boot/compressed/sev.c @@ -415,6 +415,19 @@ bool snp_init(struct boot_params *bp) if (!cc_info) return false; + /* + * If SEV-SNP-specific Confidential Computing blob is present, then + * firmware/bootloader have indicated SEV-SNP support. Verifying this + * involves CPUID checks which will be more reliable if the SEV-SNP + * CPUID table is used. See comments for snp_cpuid_info_create() for + * more details. + */ + snp_cpuid_info_create(cc_info); + + /* SEV-SNP CPUID table should be set up now. */ + if (!snp_cpuid_active()) + sev_es_terminate(1, GHCB_TERM_CPUID); + /* * Pass run-time kernel a pointer to CC info via boot_params so EFI * config table doesn't need to be searched again during early startup diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h index cd189c20bcc4..4fa7ca20d7c9 100644 --- a/arch/x86/include/asm/sev.h +++ b/arch/x86/include/asm/sev.h @@ -157,6 +157,7 @@ bool snp_init(struct boot_params *bp); * sev-shared.c via #include and these declarations can be dropped. */ struct cc_blob_sev_info *snp_find_cc_blob_setup_data(struct boot_params *bp); +void snp_cpuid_info_create(const struct cc_blob_sev_info *cc_info); #else static inline void sev_es_ist_enter(struct pt_regs *regs) { } static inline void sev_es_ist_exit(void) { } diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c index bd58a4ce29c8..5cb8f87df4b3 100644 --- a/arch/x86/kernel/sev-shared.c +++ b/arch/x86/kernel/sev-shared.c @@ -403,6 +403,23 @@ snp_cpuid_find_validated_func(u32 func, u32 subfunc, u32 *eax, u32 *ebx, return false; } +static void __init snp_cpuid_set_ranges(void) +{ + const struct snp_cpuid_info *cpuid_info = snp_cpuid_info_get_ptr(); + int i; + + for (i = 0; i < cpuid_info->count; i++) { + const struct snp_cpuid_fn *fn = &cpuid_info->fn[i]; + + if (fn->eax_in == 0x0) + cpuid_std_range_max = fn->eax; + else if (fn->eax_in == 0x40000000) + cpuid_hyp_range_max = fn->eax; + else if (fn->eax_in == 0x80000000) + cpuid_ext_range_max = fn->eax; + } +} + static bool snp_cpuid_check_range(u32 func) { if (func <= cpuid_std_range_max || @@ -968,3 +985,29 @@ snp_find_cc_blob_setup_data(struct boot_params *bp) return (struct cc_blob_sev_info *)(unsigned long)sd->cc_blob_address; } + +/* + * Initialize the kernel's copy of the SEV-SNP CPUID table, and set up the + * pointer that will be used to access it. + * + * Maintaining a direct mapping of the SEV-SNP CPUID table used by firmware + * would be possible as an alternative, but the approach is brittle since the + * mapping needs to be updated in sync with all the changes to virtual memory + * layout and related mapping facilities throughout the boot process. + */ +void __init snp_cpuid_info_create(const struct cc_blob_sev_info *cc_info) +{ + const struct snp_cpuid_info *cpuid_info_fw, *cpuid_info; + + if (!cc_info || !cc_info->cpuid_phys || cc_info->cpuid_len < PAGE_SIZE) + sev_es_terminate(1, GHCB_TERM_CPUID); + + cpuid_info_fw = (const struct snp_cpuid_info *)cc_info->cpuid_phys; + if (!cpuid_info_fw->count || cpuid_info_fw->count > SNP_CPUID_COUNT_MAX) + sev_es_terminate(1, GHCB_TERM_CPUID); + + cpuid_info = snp_cpuid_info_get_ptr(); + memcpy((void *)cpuid_info, cpuid_info_fw, sizeof(*cpuid_info)); + snp_cpuid_initialized = true; + snp_cpuid_set_ranges(); +}