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[2001:1ae9:1c2:4c00:20f:c6b4:1e57:7965]) by smtp.gmail.com with ESMTPSA id g11-20020a7bc4cb000000b003fbab76165asm8034556wmk.48.2023.06.30.04.08.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Jun 2023 04:08:38 -0700 (PDT) Date: Fri, 30 Jun 2023 13:08:37 +0200 From: Andrew Jones To: Alexandre Ghiti Cc: Jonathan Corbet , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Paul Walmsley , Palmer Dabbelt , Albert Ou , Atish Patra , Anup Patel , Will Deacon , Rob Herring , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v3 07/10] drivers: perf: Implement perf event mmap support in the SBI backend Message-ID: <20230630-ae0abe0611576cd52111903c@orel> References: <20230630083013.102334-1-alexghiti@rivosinc.com> <20230630083013.102334-8-alexghiti@rivosinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230630083013.102334-8-alexghiti@rivosinc.com> Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org On Fri, Jun 30, 2023 at 10:30:10AM +0200, Alexandre Ghiti wrote: > We used to unconditionnally expose the cycle and instret csrs to > userspace, which gives rise to security concerns. > > So now we only allow access to hw counters from userspace through the perf > framework which will handle context switches, per-task events...etc. But > as we cannot break userspace, we give the user the choice to go back to > the previous behaviour by setting the sysctl perf_user_access. > > Signed-off-by: Alexandre Ghiti > --- > drivers/perf/riscv_pmu.c | 9 +- > drivers/perf/riscv_pmu_sbi.c | 192 +++++++++++++++++++++++++++++++++-- > 2 files changed, 194 insertions(+), 7 deletions(-) > > diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c > index e1b0992f34df..80c052e93f9e 100644 > --- a/drivers/perf/riscv_pmu.c > +++ b/drivers/perf/riscv_pmu.c > @@ -38,8 +38,15 @@ void arch_perf_update_userpage(struct perf_event *event, > userpg->cap_user_time_short = 0; > userpg->cap_user_rdpmc = riscv_perf_user_access(event); > > +#ifdef CONFIG_RISCV_PMU > + /* > + * The counters are 64-bit but the priv spec doesn't mandate all the > + * bits to be implemented: that's why, counter width can vary based on > + * the cpu vendor. > + */ > if (userpg->cap_user_rdpmc) > - userpg->pmc_width = 64; > + userpg->pmc_width = to_riscv_pmu(event->pmu)->ctr_get_width(event->hw.idx) + 1; > +#endif > > do { > rd = sched_clock_read_begin(&seq); > diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c > index 83c3f1c4d2f1..acabb6c273c1 100644 > --- a/drivers/perf/riscv_pmu_sbi.c > +++ b/drivers/perf/riscv_pmu_sbi.c > @@ -24,6 +24,14 @@ > #include > #include > > +#define SYSCTL_NO_USER_ACCESS 0 > +#define SYSCTL_USER_ACCESS 1 > +#define SYSCTL_LEGACY 2 > + > +#define PERF_EVENT_FLAG_NO_USER_ACCESS BIT(SYSCTL_NO_USER_ACCESS) > +#define PERF_EVENT_FLAG_USER_ACCESS BIT(SYSCTL_USER_ACCESS) > +#define PERF_EVENT_FLAG_LEGACY BIT(SYSCTL_LEGACY) > + > PMU_FORMAT_ATTR(event, "config:0-47"); > PMU_FORMAT_ATTR(firmware, "config:63"); > > @@ -43,6 +51,9 @@ static const struct attribute_group *riscv_pmu_attr_groups[] = { > NULL, > }; > > +/* Allow user mode access by default */ > +static int sysctl_perf_user_access __read_mostly = SYSCTL_USER_ACCESS; > + > /* > * RISC-V doesn't have heterogeneous harts yet. This need to be part of > * per_cpu in case of harts with different pmu counters > @@ -301,6 +312,11 @@ int riscv_pmu_get_hpm_info(u32 *hw_ctr_width, u32 *num_hw_ctr) > } > EXPORT_SYMBOL_GPL(riscv_pmu_get_hpm_info); > > +static uint8_t pmu_sbi_csr_index(struct perf_event *event) > +{ > + return pmu_ctr_list[event->hw.idx].csr - CSR_CYCLE; > +} > + > static unsigned long pmu_sbi_get_filter_flags(struct perf_event *event) > { > unsigned long cflags = 0; > @@ -329,18 +345,34 @@ static int pmu_sbi_ctr_get_idx(struct perf_event *event) > struct cpu_hw_events *cpuc = this_cpu_ptr(rvpmu->hw_events); > struct sbiret ret; > int idx; > - uint64_t cbase = 0; > + uint64_t cbase = 0, cmask = rvpmu->cmask; > unsigned long cflags = 0; > > cflags = pmu_sbi_get_filter_flags(event); > + > + /* > + * In legacy mode, we have to force the fixed counters for those events > + * but not in the user access mode as we want to use the other counters > + * that support sampling/filtering. > + */ > + if (hwc->flags & PERF_EVENT_FLAG_LEGACY) { > + if (event->attr.config == PERF_COUNT_HW_CPU_CYCLES) { > + cflags |= SBI_PMU_CFG_FLAG_SKIP_MATCH; > + cmask = 1; > + } else if (event->attr.config == PERF_COUNT_HW_INSTRUCTIONS) { > + cflags |= SBI_PMU_CFG_FLAG_SKIP_MATCH; > + cmask = 1UL << (CSR_INSTRET - CSR_CYCLE); > + } > + } > + > /* retrieve the available counter index */ > #if defined(CONFIG_32BIT) > ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_CFG_MATCH, cbase, > - rvpmu->cmask, cflags, hwc->event_base, hwc->config, > + cmask, cflags, hwc->event_base, hwc->config, > hwc->config >> 32); > #else > ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_CFG_MATCH, cbase, > - rvpmu->cmask, cflags, hwc->event_base, hwc->config, 0); > + cmask, cflags, hwc->event_base, hwc->config, 0); > #endif > if (ret.error) { > pr_debug("Not able to find a counter for event %lx config %llx\n", > @@ -474,6 +506,14 @@ static u64 pmu_sbi_ctr_read(struct perf_event *event) > return val; > } > > +static void pmu_sbi_set_scounteren(void *arg) > +{ > + struct perf_event *event = (struct perf_event *)arg; > + > + csr_write(CSR_SCOUNTEREN, > + csr_read(CSR_SCOUNTEREN) | (1 << pmu_sbi_csr_index(event))); > +} > + > static void pmu_sbi_ctr_start(struct perf_event *event, u64 ival) > { > struct sbiret ret; > @@ -490,6 +530,18 @@ static void pmu_sbi_ctr_start(struct perf_event *event, u64 ival) > if (ret.error && (ret.error != SBI_ERR_ALREADY_STARTED)) > pr_err("Starting counter idx %d failed with error %d\n", > hwc->idx, sbi_err_map_linux_errno(ret.error)); > + > + if (hwc->flags & PERF_EVENT_FLAG_USER_ACCESS && > + hwc->flags & PERF_EVENT_FLAG_USER_READ_CNT) nit: Add () around the &'s. I thought checkpatch complained about that? > + pmu_sbi_set_scounteren((void *)event); > +} > + > +static void pmu_sbi_reset_scounteren(void *arg) > +{ > + struct perf_event *event = (struct perf_event *)arg; > + > + csr_write(CSR_SCOUNTEREN, > + csr_read(CSR_SCOUNTEREN) & ~(1 << pmu_sbi_csr_index(event))); > } nit: I'd collocate pmu_sbi_set_scounteren() and pmu_sbi_reset_scounteren() since they're counterparts. > > static void pmu_sbi_ctr_stop(struct perf_event *event, unsigned long flag) > @@ -497,6 +549,10 @@ static void pmu_sbi_ctr_stop(struct perf_event *event, unsigned long flag) > struct sbiret ret; > struct hw_perf_event *hwc = &event->hw; > > + if (hwc->flags & PERF_EVENT_FLAG_USER_ACCESS && > + hwc->flags & PERF_EVENT_FLAG_USER_READ_CNT) nit: () around &'s > + pmu_sbi_reset_scounteren((void *)event); > + > ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, hwc->idx, 1, flag, 0, 0, 0); > if (ret.error && (ret.error != SBI_ERR_ALREADY_STOPPED) && > flag != SBI_PMU_STOP_FLAG_RESET) > @@ -704,10 +760,13 @@ static int pmu_sbi_starting_cpu(unsigned int cpu, struct hlist_node *node) > struct cpu_hw_events *cpu_hw_evt = this_cpu_ptr(pmu->hw_events); > > /* > - * Enable the access for CYCLE, TIME, and INSTRET CSRs from userspace, > - * as is necessary to maintain uABI compatibility. > + * We keep enabling userspace access to CYCLE, TIME and INSRET via the > + * legacy option but that will be removed in the future. > */ > - csr_write(CSR_SCOUNTEREN, 0x7); > + if (sysctl_perf_user_access == SYSCTL_LEGACY) > + csr_write(CSR_SCOUNTEREN, 0x7); > + else > + csr_write(CSR_SCOUNTEREN, 0x2); > > /* Stop all the counters so that they can be enabled from perf */ > pmu_sbi_stop_all(pmu); > @@ -851,6 +910,121 @@ static void riscv_pmu_destroy(struct riscv_pmu *pmu) > cpuhp_state_remove_instance(CPUHP_AP_PERF_RISCV_STARTING, &pmu->node); > } > > +static void pmu_sbi_event_init(struct perf_event *event) > +{ > + /* > + * The permissions are set at event_init so that we do not depend > + * on the sysctl value that can change. > + */ > + if (sysctl_perf_user_access == SYSCTL_NO_USER_ACCESS) > + event->hw.flags |= PERF_EVENT_FLAG_NO_USER_ACCESS; > + else if (sysctl_perf_user_access == SYSCTL_USER_ACCESS) > + event->hw.flags |= PERF_EVENT_FLAG_USER_ACCESS; > + else > + event->hw.flags |= PERF_EVENT_FLAG_LEGACY; > +} > + > +static void pmu_sbi_event_mapped(struct perf_event *event, struct mm_struct *mm) > +{ > + if (event->hw.flags & PERF_EVENT_FLAG_NO_USER_ACCESS) > + return; > + > + if (event->hw.flags & PERF_EVENT_FLAG_LEGACY) { > + if (event->attr.config != PERF_COUNT_HW_CPU_CYCLES && > + event->attr.config != PERF_COUNT_HW_INSTRUCTIONS) { > + return; > + } > + } > + > + /* > + * The user mmapped the event to directly access it: this is where > + * we determine based on sysctl_perf_user_access if we grant userspace > + * the direct access to this event. That means that within the same > + * task, some events may be directly accessible and some other may not, > + * if the user changes the value of sysctl_perf_user_accesss in the > + * meantime. > + */ > + > + event->hw.flags |= PERF_EVENT_FLAG_USER_READ_CNT; > + > + /* > + * We must enable userspace access *before* advertising in the user page > + * that it is possible to do so to avoid any race. > + * And we must notify all cpus here because threads that currently run > + * on other cpus will try to directly access the counter too without > + * calling pmu_sbi_ctr_start. > + */ > + if (event->hw.flags & PERF_EVENT_FLAG_USER_ACCESS) > + on_each_cpu_mask(mm_cpumask(mm), > + pmu_sbi_set_scounteren, (void *)event, 1); > +} > + > +static void pmu_sbi_event_unmapped(struct perf_event *event, struct mm_struct *mm) > +{ > + if (event->hw.flags & PERF_EVENT_FLAG_NO_USER_ACCESS) > + return; > + > + if (event->hw.flags & PERF_EVENT_FLAG_LEGACY) { > + if (event->attr.config != PERF_COUNT_HW_CPU_CYCLES && > + event->attr.config != PERF_COUNT_HW_INSTRUCTIONS) { > + return; > + } > + } > + > + /* > + * Here we can directly remove user access since the user does not have > + * access to the user page anymore so we avoid the racy window where the > + * user could have read cap_user_rdpmc to true right before we disable > + * it. > + */ > + event->hw.flags &= ~PERF_EVENT_FLAG_USER_READ_CNT; > + > + if (event->hw.flags & PERF_EVENT_FLAG_USER_ACCESS) > + on_each_cpu_mask(mm_cpumask(mm), > + pmu_sbi_reset_scounteren, (void *)event, 1); > +} > + > +static void riscv_pmu_update_counter_access(void *info) > +{ > + if (sysctl_perf_user_access == SYSCTL_LEGACY) > + csr_write(CSR_SCOUNTEREN, 0x7); > + else > + csr_write(CSR_SCOUNTEREN, 0x2); > +} > + > +static int riscv_pmu_proc_user_access_handler(struct ctl_table *table, > + int write, void *buffer, > + size_t *lenp, loff_t *ppos) > +{ > + int prev = sysctl_perf_user_access; > + int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); > + > + /* > + * Test against the previous value since we clear SCOUNTEREN when > + * sysctl_perf_user_access is set to SYSCTL_USER_ACCESS, but we should > + * not do that if that was already the case. > + */ > + if (ret || !write || prev == sysctl_perf_user_access) > + return ret; > + > + on_each_cpu(riscv_pmu_update_counter_access, NULL, 1); > + > + return 0; > +} > + > +static struct ctl_table sbi_pmu_sysctl_table[] = { > + { > + .procname = "perf_user_access", > + .data = &sysctl_perf_user_access, > + .maxlen = sizeof(unsigned int), > + .mode = 0644, > + .proc_handler = riscv_pmu_proc_user_access_handler, > + .extra1 = SYSCTL_ZERO, > + .extra2 = SYSCTL_TWO, > + }, > + { } > +}; > + > static int pmu_sbi_device_probe(struct platform_device *pdev) > { > struct riscv_pmu *pmu = NULL; > @@ -888,6 +1062,10 @@ static int pmu_sbi_device_probe(struct platform_device *pdev) > pmu->ctr_get_width = pmu_sbi_ctr_get_width; > pmu->ctr_clear_idx = pmu_sbi_ctr_clear_idx; > pmu->ctr_read = pmu_sbi_ctr_read; > + pmu->event_init = pmu_sbi_event_init; > + pmu->event_mapped = pmu_sbi_event_mapped; > + pmu->event_unmapped = pmu_sbi_event_unmapped; > + pmu->csr_index = pmu_sbi_csr_index; > > ret = cpuhp_state_add_instance(CPUHP_AP_PERF_RISCV_STARTING, &pmu->node); > if (ret) > @@ -901,6 +1079,8 @@ static int pmu_sbi_device_probe(struct platform_device *pdev) > if (ret) > goto out_unregister; > > + register_sysctl("kernel", sbi_pmu_sysctl_table); > + > return 0; > > out_unregister: > -- > 2.39.2 > Other than the nits, Reviewed-by: Andrew Jones Thanks, drew