Hi Deepak
On Thu, Nov 14, 2024 at 9:06 AM Deepak Gupta debug@rivosinc.com 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 debug@rivosinc.com 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 debug@rivosinc.com
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_FWFTli a6, SBI_EXT_FWFT_SETli a0, SBI_FWFT_SHADOW_STACKli a1, 1 /* enable supervisor to access shadow stack access */li a2, SBI_FWFT_SET_FLAG_LOCKecall 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_FWFTli a6, SBI_EXT_FWFT_SETli a0, SBI_FWFT_SHADOW_STACKli a1, 1 /* enable supervisor to access shadow stack access */li a2, SBI_FWFT_SET_FLAG_LOCKecall 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;
Regards, Nick
Regards, Nick
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