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AJvYcCUVejQAJ7Drjig/LjVVsxS/XF3kFEHnn5OZWSFdx7OpVR6F0dqy484tABrQU1reL3qp/gy3m8rrsA==@kvack.org X-Gm-Message-State: AOJu0YyyTuZjAG2K0oBMzcEly85jisFA1CoTI9kiPlKXwRafARWmGPOR 4ZsLC88LQrXn0ACX17GfQeaJ6RksaMBMbq661TK+WQY0k5eHYzES5QDLAYzjghA= X-Google-Smtp-Source: AGHT+IFYV+lyD6AUZ64wWkmaKdb2jE8s1l+YlxE25IyFaRji6Gg+al5X5KNPM0lWiRmirmHIFmzF1w== X-Received: by 2002:a05:6808:2222:b0:3e6:22f:ea48 with SMTP id 5614622812f47-3e7b7bdede7mr481448b6e.28.1731547504098; Wed, 13 Nov 2024 17:25:04 -0800 (PST) Received: from debug.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-7f41f5bcad0sm11125410a12.32.2024.11.13.17.25.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Nov 2024 17:25:03 -0800 (PST) Date: Wed, 13 Nov 2024 17:25:00 -0800 From: Deepak Gupta To: Nick Hu Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Lorenzo Stoakes , Paul Walmsley , Palmer Dabbelt , Albert Ou , Conor Dooley , Rob Herring , Krzysztof Kozlowski , Arnd Bergmann , Christian Brauner , Peter Zijlstra , Oleg Nesterov , Eric Biederman , Kees Cook , Jonathan Corbet , Shuah Khan , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, alistair.francis@wdc.com, richard.henderson@linaro.org, jim.shu@sifive.com, andybnac@gmail.com, kito.cheng@sifive.com, charlie@rivosinc.com, atishp@rivosinc.com, evan@rivosinc.com, cleger@rivosinc.com, alexghiti@rivosinc.com, samitolvanen@google.com, broonie@kernel.org, rick.p.edgecombe@intel.com Subject: Re: [PATCH v8 24/29] riscv: enable kernel access to shadow stack memory via FWFT sbi call Message-ID: References: <20241111-v5_user_cfi_series-v8-0-dce14aa30207@rivosinc.com> <20241111-v5_user_cfi_series-v8-24-dce14aa30207@rivosinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: cjndo85rzn7qytness4pxewowswk8865 X-Rspam-User: X-Rspamd-Queue-Id: 88B441A0019 X-Rspamd-Server: rspam02 X-HE-Tag: 1731547450-523574 X-HE-Meta: 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 KiEUUAgb 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Nov 14, 2024 at 09:20:14AM +0800, Nick Hu wrote: >Hi Deepak > >On Thu, Nov 14, 2024 at 9:06 AM Deepak Gupta wrote: >> >> On Thu, Nov 14, 2024 at 12:13:38AM +0800, Nick Hu wrote: >> >Hi Deepak >> > >> >On Tue, Nov 12, 2024 at 5:08 AM Deepak Gupta wrote: >> >> >> >> Kernel will have to perform shadow stack operations on user shadow stack. >> >> Like during signal delivery and sigreturn, shadow stack token must be >> >> created and validated respectively. Thus shadow stack access for kernel >> >> must be enabled. >> >> >> >> In future when kernel shadow stacks are enabled for linux kernel, it must >> >> be enabled as early as possible for better coverage and prevent imbalance >> >> between regular stack and shadow stack. After `relocate_enable_mmu` has >> >> been done, this is as early as possible it can enabled. >> >> >> >> Signed-off-by: Deepak Gupta >> >> --- >> >> arch/riscv/kernel/asm-offsets.c | 4 ++++ >> >> arch/riscv/kernel/head.S | 12 ++++++++++++ >> >> 2 files changed, 16 insertions(+) >> >> >> >> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c >> >> index 766bd33f10cb..a22ab8a41672 100644 >> >> --- a/arch/riscv/kernel/asm-offsets.c >> >> +++ b/arch/riscv/kernel/asm-offsets.c >> >> @@ -517,4 +517,8 @@ void asm_offsets(void) >> >> DEFINE(FREGS_A6, offsetof(struct ftrace_regs, a6)); >> >> DEFINE(FREGS_A7, offsetof(struct ftrace_regs, a7)); >> >> #endif >> >> + DEFINE(SBI_EXT_FWFT, SBI_EXT_FWFT); >> >> + DEFINE(SBI_EXT_FWFT_SET, SBI_EXT_FWFT_SET); >> >> + DEFINE(SBI_FWFT_SHADOW_STACK, SBI_FWFT_SHADOW_STACK); >> >> + DEFINE(SBI_FWFT_SET_FLAG_LOCK, SBI_FWFT_SET_FLAG_LOCK); >> >> } >> >> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S >> >> index 356d5397b2a2..6244408ca917 100644 >> >> --- a/arch/riscv/kernel/head.S >> >> +++ b/arch/riscv/kernel/head.S >> >> @@ -164,6 +164,12 @@ secondary_start_sbi: >> >> call relocate_enable_mmu >> >> #endif >> >> call .Lsetup_trap_vector >> >> + li a7, SBI_EXT_FWFT >> >> + li a6, SBI_EXT_FWFT_SET >> >> + li a0, SBI_FWFT_SHADOW_STACK >> >> + li a1, 1 /* enable supervisor to access shadow stack access */ >> >> + li a2, SBI_FWFT_SET_FLAG_LOCK >> >> + ecall >> >> scs_load_current >> >> call smp_callin >> >> #endif /* CONFIG_SMP */ >> >> @@ -320,6 +326,12 @@ SYM_CODE_START(_start_kernel) >> >> la tp, init_task >> >> la sp, init_thread_union + THREAD_SIZE >> >> addi sp, sp, -PT_SIZE_ON_STACK >> >> + li a7, SBI_EXT_FWFT >> >> + li a6, SBI_EXT_FWFT_SET >> >> + li a0, SBI_FWFT_SHADOW_STACK >> >> + li a1, 1 /* enable supervisor to access shadow stack access */ >> >> + li a2, SBI_FWFT_SET_FLAG_LOCK >> >> + ecall >> >> scs_load_current >> >> >> >> #ifdef CONFIG_KASAN >> >> >> >> -- >> >> 2.45.0 >> >> >> >Should we clear the SBI_FWFT_SET_FLAG_LOCK before the cpu hotplug >> >otherwise the menvcfg.sse won't be set by the fwft set sbi call when >> >the hotplug cpu back to kernel? >> >> Hmm... >> >> An incoming hotplug CPU has no features setup on it. >> I see that `sbi_cpu_start` will supply `secondary_start_sbi` as start >> up code for incoming CPU. `secondary_start_sbi` is in head.S which converges >> in `.Lsecondary_start_common`. And thus hotplugged CPU should be >> issuing shadow stack set FWFT sbi as well. >> >> Am I missing something ? >> >This is the correct flow. However the opensbi will deny it due to the >SBI_FWFT_SET_FLAG_LOCK already being set. >So the menvcfg.sse will not set by this flow. > >if (conf->flags & SBI_FWFT_SET_FLAG_LOCK) > return SBI_EDENIED; > hmm... Why? `conf` is pointing to per-hart state in firmware. On this incoming cpu, opensbi (or equivalent) firmware must have ensured that this per-hart state doesn't have lock set. Am I missing something? >Regards, >Nick >> > >> >Regards, >> >Nick >> >> >> >> _______________________________________________ >> >> linux-riscv mailing list >> >> linux-riscv@lists.infradead.org >> >> http://lists.infradead.org/mailman/listinfo/linux-riscv