Track FF-A version negotiation per VM and enforce that no FF-A ABI (other than FFA_VERSION) is processed before a guest has selected a version.
Each ffa_ctx gains a dedicated guest_vers_lock, a negotiated version (guest_vers) and a guest_vers_tmp: - guest_vers is the version negotiated or 0 if no version has been negotiated. This must be used with ACCESS_ONCE when reading it without the spinlock taken. - guest_vers_tmp stores the version currently requested by a VM. The version requested is the one actually negotiated once a call different from FFA_VERSION is done to allow several attempts and as requested by FF-A specification. We always return our implementation version FFA_MY_VERSION, even if the version requested was different, as requested by FF-A specification. Any call other than FFA_VERSION is rejected until a version has been requested. Update all places in the code where guest_vers is used to use ACCESS_ONCE. This prevents partially initialised contexts from using the mediator and complies with the FF-A 1.2 FFA_VERSION semantics. Signed-off-by: Bertrand Marquis <[email protected]> --- Changes in v1: - remove the guest_vers_negotiated and use guest_vers = 0 as condition for a version being negotiated instead - introduce guest_vers_tmp to store a requested version until it is becoming the one negotiated. - remove not needed if negotiated condition. - use ACCESS_ONCE when reading guest_vers and use guest_vers == 0 as condition for a version being negotiated. - Update FF-A version handling comment in ffa_private.h --- xen/arch/arm/tee/ffa.c | 101 +++++++++++++++++++++++++------- xen/arch/arm/tee/ffa_msg.c | 2 +- xen/arch/arm/tee/ffa_partinfo.c | 4 +- xen/arch/arm/tee/ffa_private.h | 26 ++++++-- xen/arch/arm/tee/ffa_shm.c | 3 +- 5 files changed, 105 insertions(+), 31 deletions(-) diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c index 2b4e24750d52..aadd6c21e7f2 100644 --- a/xen/arch/arm/tee/ffa.c +++ b/xen/arch/arm/tee/ffa.c @@ -158,31 +158,38 @@ static bool ffa_abi_supported(uint32_t id) return !ffa_simple_call(FFA_FEATURES, id, 0, 0, 0); } -static void handle_version(struct cpu_user_regs *regs) +static bool ffa_negotiate_version(struct cpu_user_regs *regs) { struct domain *d = current->domain; struct ffa_ctx *ctx = d->arch.tee; - uint32_t vers = get_user_reg(regs, 1); - uint32_t old_vers; + uint32_t fid = get_user_reg(regs, 0); + uint32_t in_vers = get_user_reg(regs, 1); + uint32_t out_vers = FFA_MY_VERSION; - /* - * Guest will use the version it requested if it is our major and minor - * lower or equals to ours. If the minor is greater, our version will be - * used. - * In any case return our version to the caller. - */ - if ( FFA_VERSION_MAJOR(vers) == FFA_MY_VERSION_MAJOR ) + spin_lock(&ctx->guest_vers_lock); + + /* If negotiation already published, continue without handling. */ + if ( ACCESS_ONCE(ctx->guest_vers) ) + goto out_continue; + + if ( fid != FFA_VERSION ) { - spin_lock(&ctx->lock); - old_vers = ctx->guest_vers; + if ( !ctx->guest_vers_tmp ) + { + out_vers = 0; + goto out_handled; + } - if ( FFA_VERSION_MINOR(vers) > FFA_MY_VERSION_MINOR ) - ctx->guest_vers = FFA_MY_VERSION; - else - ctx->guest_vers = vers; - spin_unlock(&ctx->lock); + /* + * A successful FFA_VERSION call does not freeze negotiation. Guests + * are allowed to issue multiple FFA_VERSION attempts (e.g. probing + * several minor versions). Negotiation becomes final only when a + * non-VERSION ABI is invoked, as required by the FF-A specification. + * Finalize negotiation: publish guest_vers once, then never change. + */ + ACCESS_ONCE(ctx->guest_vers) = ctx->guest_vers_tmp; - if ( IS_ENABLED(CONFIG_FFA_VM_TO_VM) && !old_vers ) + if ( IS_ENABLED(CONFIG_FFA_VM_TO_VM) ) { /* One more VM with FF-A support available */ inc_ffa_vm_count(); @@ -190,8 +197,48 @@ static void handle_version(struct cpu_user_regs *regs) list_add_tail(&ctx->ctx_list, &ffa_ctx_head); write_unlock(&ffa_ctx_list_rwlock); } + + goto out_continue; } - ffa_set_regs(regs, FFA_MY_VERSION, 0, 0, 0, 0, 0, 0, 0); + + /* + * guest_vers_tmp stores the version selected by the guest (lower minor may + * require reduced data structures). However, the value returned to the + * guest via FFA_VERSION is always FFA_MY_VERSION, the implementation + * version, as required by FF-A. The two values intentionally differ. + */ + + /* + * Return our highest implementation version on request different than our + * major and mark negotiated version as our implementation version. + */ + if ( FFA_VERSION_MAJOR(in_vers) != FFA_MY_VERSION_MAJOR ) + { + ctx->guest_vers_tmp = FFA_MY_VERSION; + goto out_handled; + } + + /* + * Use our minor version if a greater minor was requested or the requested + * minor if it is lower than ours was requested. + */ + if ( FFA_VERSION_MINOR(in_vers) > FFA_MY_VERSION_MINOR ) + ctx->guest_vers_tmp = FFA_MY_VERSION; + else + ctx->guest_vers_tmp = in_vers; + +out_handled: + spin_unlock(&ctx->guest_vers_lock); + if ( out_vers ) + ffa_set_regs(regs, out_vers, 0, 0, 0, 0, 0, 0, 0); + else + ffa_set_regs_error(regs, FFA_RET_NOT_SUPPORTED); + return true; + +out_continue: + spin_unlock(&ctx->guest_vers_lock); + + return false; } static void handle_features(struct cpu_user_regs *regs) @@ -274,10 +321,17 @@ static bool ffa_handle_call(struct cpu_user_regs *regs) if ( !ctx ) return false; + /* A version must be negotiated first */ + if ( !ACCESS_ONCE(ctx->guest_vers) ) + { + if ( ffa_negotiate_version(regs) ) + return true; + } + switch ( fid ) { case FFA_VERSION: - handle_version(regs); + ffa_set_regs(regs, FFA_MY_VERSION, 0, 0, 0, 0, 0, 0, 0); return true; case FFA_ID_GET: ffa_set_regs_success(regs, ffa_get_vm_id(d), 0); @@ -371,6 +425,11 @@ static int ffa_domain_init(struct domain *d) d->arch.tee = ctx; ctx->teardown_d = d; INIT_LIST_HEAD(&ctx->shm_list); + spin_lock_init(&ctx->lock); + spin_lock_init(&ctx->guest_vers_lock); + ctx->guest_vers = 0; + ctx->guest_vers_tmp = 0; + INIT_LIST_HEAD(&ctx->ctx_list); ctx->ffa_id = ffa_get_vm_id(d); ctx->num_vcpus = d->max_vcpus; @@ -452,7 +511,7 @@ static int ffa_domain_teardown(struct domain *d) if ( !ctx ) return 0; - if ( IS_ENABLED(CONFIG_FFA_VM_TO_VM) && ctx->guest_vers ) + if ( IS_ENABLED(CONFIG_FFA_VM_TO_VM) && ACCESS_ONCE(ctx->guest_vers) ) { dec_ffa_vm_count(); write_lock(&ffa_ctx_list_rwlock); diff --git a/xen/arch/arm/tee/ffa_msg.c b/xen/arch/arm/tee/ffa_msg.c index c20c5bec0f76..2c2ebc9c5cd6 100644 --- a/xen/arch/arm/tee/ffa_msg.c +++ b/xen/arch/arm/tee/ffa_msg.c @@ -113,7 +113,7 @@ static int32_t ffa_msg_send2_vm(uint16_t dst_id, const void *src_buf, } dst_ctx = dst_d->arch.tee; - if ( !dst_ctx->guest_vers ) + if ( !ACCESS_ONCE(dst_ctx->guest_vers) ) { ret = FFA_RET_INVALID_PARAMETERS; goto out_unlock; diff --git a/xen/arch/arm/tee/ffa_partinfo.c b/xen/arch/arm/tee/ffa_partinfo.c index fa56b1587e3b..ec5a53ed1cab 100644 --- a/xen/arch/arm/tee/ffa_partinfo.c +++ b/xen/arch/arm/tee/ffa_partinfo.c @@ -238,7 +238,7 @@ void ffa_handle_partition_info_get(struct cpu_user_regs *regs) * use the v1.0 structure size in the destination buffer. * Otherwise use the size of the highest version we support, here 1.1. */ - if ( ctx->guest_vers == FFA_VERSION_1_0 ) + if ( ACCESS_ONCE(ctx->guest_vers) == FFA_VERSION_1_0 ) dst_size = sizeof(struct ffa_partition_info_1_0); else dst_size = sizeof(struct ffa_partition_info_1_1); @@ -250,7 +250,7 @@ void ffa_handle_partition_info_get(struct cpu_user_regs *regs) * FF-A v1.0 has w5 MBZ while v1.1 allows * FFA_PARTITION_INFO_GET_COUNT_FLAG to be non-zero. */ - if ( ctx->guest_vers == FFA_VERSION_1_0 || + if ( ACCESS_ONCE(ctx->guest_vers) == FFA_VERSION_1_0 || flags != FFA_PARTITION_INFO_GET_COUNT_FLAG ) { ret = FFA_RET_INVALID_PARAMETERS; diff --git a/xen/arch/arm/tee/ffa_private.h b/xen/arch/arm/tee/ffa_private.h index 8d01da0009d3..4e4ac7fd7bc4 100644 --- a/xen/arch/arm/tee/ffa_private.h +++ b/xen/arch/arm/tee/ffa_private.h @@ -355,12 +355,6 @@ struct ffa_ctx { * Global data accessed with lock locked. */ spinlock_t lock; - /* - * FF-A version negotiated by the guest, only modifications to - * this field are done with the lock held as this is expected to - * be done once at init by a guest. - */ - uint32_t guest_vers; /* Number of 4kB pages in each of rx/rx_pg and tx/tx_pg */ unsigned int page_count; /* Number of allocated shared memory object */ @@ -368,6 +362,26 @@ struct ffa_ctx { /* Used shared memory objects, struct ffa_shm_mem */ struct list_head shm_list; + /* + * FF-A version handling + * guest_vers is the single published negotiated version. It is 0 until + * negotiation completes, after which it is set once and never changes. + * Negotiation uses guest_vers_tmp under guest_vers_lock; when a + * non-VERSION ABI is invoked, Xen finalizes negotiation by publishing + * guest_vers using ACCESS_ONCE() store. + * Readers use ACCESS_ONCE(guest_vers) != 0 to detect availability and + * can consume guest_vers without barriers because it never changes once + * published. + */ + spinlock_t guest_vers_lock; + /* + * Published negotiated version. Zero means "not negotiated yet". + * Once non-zero, it never changes. + */ + uint32_t guest_vers; + /* Temporary version used during negotiation under guest_vers_lock */ + uint32_t guest_vers_tmp; + /* * Rx buffer, accessed with rx_lock locked. * rx_is_free is used to serialize access. diff --git a/xen/arch/arm/tee/ffa_shm.c b/xen/arch/arm/tee/ffa_shm.c index d628c1b70609..dad3da192247 100644 --- a/xen/arch/arm/tee/ffa_shm.c +++ b/xen/arch/arm/tee/ffa_shm.c @@ -495,7 +495,8 @@ void ffa_handle_mem_share(struct cpu_user_regs *regs) if ( frag_len > ctx->page_count * FFA_PAGE_SIZE ) goto out_unlock; - ret = read_mem_transaction(ctx->guest_vers, ctx->tx, frag_len, &trans); + ret = read_mem_transaction(ACCESS_ONCE(ctx->guest_vers), ctx->tx, + frag_len, &trans); if ( ret ) goto out_unlock; -- 2.51.2
