Messages in this thread | | | Date | Thu, 20 Jan 2022 09:50:09 +0100 | Subject | Re: [RFC PATCH v1 02/10] KVM: s390: Honor storage keys when accessing guest memory | From | Christian Borntraeger <> |
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Am 20.01.22 um 09:11 schrieb Janis Schoetterl-Glausch: > On 1/19/22 20:27, Christian Borntraeger wrote: >> Am 18.01.22 um 10:52 schrieb Janis Schoetterl-Glausch: >>> Storage key checking had not been implemented for instructions emulated >>> by KVM. Implement it by enhancing the functions used for guest access, >>> in particular those making use of access_guest which has been renamed >>> to access_guest_with_key. >>> Accesses via access_guest_real should not be key checked. >>> >>> For actual accesses, key checking is done by __copy_from/to_user_with_key >>> (which internally uses MVCOS/MVCP/MVCS). >>> In cases where accessibility is checked without an actual access, >>> this is performed by getting the storage key and checking >>> if the access key matches. >>> In both cases, if applicable, storage and fetch protection override >>> are honored. >>> >>> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com> >>> --- >>> arch/s390/include/asm/ctl_reg.h | 2 + >>> arch/s390/include/asm/page.h | 2 + >>> arch/s390/kvm/gaccess.c | 174 +++++++++++++++++++++++++++++--- >>> arch/s390/kvm/gaccess.h | 78 ++++++++++++-- >>> arch/s390/kvm/intercept.c | 12 +-- >>> arch/s390/kvm/kvm-s390.c | 4 +- >>> 6 files changed, 241 insertions(+), 31 deletions(-) >>> >>> diff --git a/arch/s390/include/asm/ctl_reg.h b/arch/s390/include/asm/ctl_reg.h >>> index 04dc65f8901d..c800199a376b 100644 >>> --- a/arch/s390/include/asm/ctl_reg.h >>> +++ b/arch/s390/include/asm/ctl_reg.h >>> @@ -12,6 +12,8 @@ >>> #define CR0_CLOCK_COMPARATOR_SIGN BIT(63 - 10) >>> #define CR0_LOW_ADDRESS_PROTECTION BIT(63 - 35) >>> +#define CR0_FETCH_PROTECTION_OVERRIDE BIT(63 - 38) >>> +#define CR0_STORAGE_PROTECTION_OVERRIDE BIT(63 - 39) >>> #define CR0_EMERGENCY_SIGNAL_SUBMASK BIT(63 - 49) >>> #define CR0_EXTERNAL_CALL_SUBMASK BIT(63 - 50) >>> #define CR0_CLOCK_COMPARATOR_SUBMASK BIT(63 - 52) >>> diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.h >>> index d98d17a36c7b..cfc4d6fb2385 100644 >>> --- a/arch/s390/include/asm/page.h >>> +++ b/arch/s390/include/asm/page.h >>> @@ -20,6 +20,8 @@ >>> #define PAGE_SIZE _PAGE_SIZE >>> #define PAGE_MASK _PAGE_MASK >>> #define PAGE_DEFAULT_ACC 0 >>> +/* storage-protection override */ >>> +#define PAGE_SPO_ACC 9 >>> #define PAGE_DEFAULT_KEY (PAGE_DEFAULT_ACC << 4) >>> #define HPAGE_SHIFT 20 >>> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c >>> index 4460808c3b9a..92ab96d55504 100644 >>> --- a/arch/s390/kvm/gaccess.c >>> +++ b/arch/s390/kvm/gaccess.c >>> @@ -10,6 +10,7 @@ >>> #include <linux/mm_types.h> >>> #include <linux/err.h> >>> #include <linux/pgtable.h> >>> +#include <linux/bitfield.h> >>> #include <asm/gmap.h> >>> #include "kvm-s390.h" >>> @@ -794,6 +795,79 @@ static int low_address_protection_enabled(struct kvm_vcpu *vcpu, >>> return 1; >>> } >>> +static bool fetch_prot_override_applicable(struct kvm_vcpu *vcpu, enum gacc_mode mode, >>> + union asce asce) >>> +{ >>> + psw_t *psw = &vcpu->arch.sie_block->gpsw; >>> + unsigned long override; >>> + >>> + if (mode == GACC_FETCH || mode == GACC_IFETCH) { >>> + /* check if fetch protection override enabled */ >>> + override = vcpu->arch.sie_block->gcr[0]; >>> + override &= CR0_FETCH_PROTECTION_OVERRIDE; >>> + /* not applicable if subject to DAT && private space */ >>> + override = override && !(psw_bits(*psw).dat && asce.p); >>> + return override; >>> + } >>> + return false; >>> +} >>> + >>> +static bool fetch_prot_override_applies(unsigned long ga, unsigned int len) >>> +{ >>> + return ga < 2048 && ga + len <= 2048; >>> +} >>> + >>> +static bool storage_prot_override_applicable(struct kvm_vcpu *vcpu) >>> +{ >>> + /* check if storage protection override enabled */ >>> + return vcpu->arch.sie_block->gcr[0] & CR0_STORAGE_PROTECTION_OVERRIDE; >>> +} >>> + >>> +static bool storage_prot_override_applies(char access_control) >>> +{ >>> + /* matches special storage protection override key (9) -> allow */ >>> + return access_control == PAGE_SPO_ACC; >>> +} >>> + >>> +static int vcpu_check_access_key(struct kvm_vcpu *vcpu, char access_key, >>> + enum gacc_mode mode, union asce asce, gpa_t gpa, >>> + unsigned long ga, unsigned int len) >>> +{ >>> + unsigned char storage_key, access_control; >>> + unsigned long hva; >>> + int r; >>> + >>> + /* access key 0 matches any storage key -> allow */ >>> + if (access_key == 0) >>> + return 0; >>> + /* >>> + * caller needs to ensure that gfn is accessible, so we can >>> + * assume that this cannot fail >>> + */ >>> + hva = gfn_to_hva(vcpu->kvm, gpa_to_gfn(gpa)); >>> + mmap_read_lock(current->mm); >>> + r = get_guest_storage_key(current->mm, hva, &storage_key); >>> + mmap_read_unlock(current->mm); >>> + if (r) >>> + return r; >>> + access_control = FIELD_GET(_PAGE_ACC_BITS, storage_key); >>> + /* access key matches storage key -> allow */ >>> + if (access_control == access_key) >>> + return 0; >>> + if (mode == GACC_FETCH || mode == GACC_IFETCH) { >>> + /* mismatching keys, no fetch protection -> allowed */ >>> + if (!(storage_key & _PAGE_FP_BIT)) >>> + return 0; >>> + if (fetch_prot_override_applicable(vcpu, mode, asce)) >>> + if (fetch_prot_override_applies(ga, len)) >>> + return 0; >>> + } >>> + if (storage_prot_override_applicable(vcpu)) >>> + if (storage_prot_override_applies(access_control)) >>> + return 0; >>> + return PGM_PROTECTION; >>> +} >> >> This function is just a pre-check (and early-exit) and we do an additional final check >> in the MVCOS routing later on, correct? It might actually be faster to get rid of this > > No, this exists for those cases that do not do an actual access, that is MEMOPs with > the check only flag, as well as the TEST PROTECTION emulation. access_guest_with_key > passes key 0 so we take the early return. It's easy to miss so Janosch suggested a comment there.
Dont we always call it in guest_range_to_gpas, which is also called for the memory access in access_guest_with_key?
> >> pre-test and simply rely on MVCOS. MVCOS is usually just some cycles while ISKE to read >> the key is really slow path and take hundreds of cycles. This would even simplify the >> patch (assuming that we do proper key checking all the time). >
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