Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 16 Jun 2021 21:55:29 -0700 (PDT)
Subject:     Re: [PATCH -next] riscv: add VMAP_STACK overflow detection
In-Reply-To: <mhng-f59de097-dd42-480a-9755-478037f44fbc@palmerdabbelt-glaptop>
CC:     Paul Walmsley <paul.walmsley@sifive.com>, aou@eecs.berkeley.edu,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     tongtiangen@huawei.com
Message-ID: <mhng-ff73351b-630a-43fb-b73b-7164a12bed26@palmerdabbelt-glaptop>
Mime-Version: 1.0 (MHng)
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

On Fri, 11 Jun 2021 20:55:45 PDT (-0700), Palmer Dabbelt wrote:
> On Thu, 03 Jun 2021 05:49:54 PDT (-0700), tongtiangen@huawei.com wrote:
>> Hi Paul & Palmer & Albert :
>>
>>      kindly ping...
>
> Sorry about that.  I remember having read this before, I'm not sure what
> happened though.  It's on for-next now.

This fails my tests for STRICT_KERNEL_RWX=n, which is probably why 
didn't get around to merging it in the first place.  

Sorry to flip-flop on you here, but I'm going to pull this off for-next.  
I know I've done that a few times lately, it's not how I'd like to be 
doing things but this cycle just ended up in a lot of distractions.

>
> Thanks!
>
>>
>>
>> On 2021/5/24 21:54, tongtiangen wrote:
>>> This patch adds stack overflow detection to riscv, usable when
>>> CONFIG_VMAP_STACK=y.
>>>
>>> Overflow is detected in kernel exception entry(kernel/entry.S), if the kernel
>>> stack is overflow and been detected, the overflow handler is invoked on a
>>> per-cpu overflow stack. This approach preserves GPRs and the original exception
>>> information.
>>>
>>> The overflow detect is performed before any attempt is made to access the stack
>>> and the principle of stack overflow detection: kernel stacks are aligned to
>>> double their size, enabling overflow to be detected with a single bit test. For
>>> example, a 16K stack is aligned to 32K, ensuring that bit 14 of the SP must be
>>> zero. On an overflow (or underflow), this bit is flipped. Thus, overflow (of
>>> less than the size of the stack) can be detected by testing whether this bit is
>>> set.
>>>
>>> This gives us a useful error message on stack overflow, as can be trigger with
>>> the LKDTM overflow test:
>>>
>>> [  388.053267] lkdtm: Performing direct entry EXHAUST_STACK
>>> [  388.053663] lkdtm: Calling function with 1024 frame size to depth 32 ...
>>> [  388.054016] lkdtm: loop 32/32 ...
>>> [  388.054186] lkdtm: loop 31/32 ...
>>> [  388.054491] lkdtm: loop 30/32 ...
>>> [  388.054672] lkdtm: loop 29/32 ...
>>> [  388.054859] lkdtm: loop 28/32 ...
>>> [  388.055010] lkdtm: loop 27/32 ...
>>> [  388.055163] lkdtm: loop 26/32 ...
>>> [  388.055309] lkdtm: loop 25/32 ...
>>> [  388.055481] lkdtm: loop 24/32 ...
>>> [  388.055653] lkdtm: loop 23/32 ...
>>> [  388.055837] lkdtm: loop 22/32 ...
>>> [  388.056015] lkdtm: loop 21/32 ...
>>> [  388.056188] lkdtm: loop 20/32 ...
>>> [  388.058145] Insufficient stack space to handle exception!
>>> [  388.058153] Task stack:     [0xffffffd014260000..0xffffffd014264000]
>>> [  388.058160] Overflow stack: [0xffffffe1f8d2c220..0xffffffe1f8d2d220]
>>> [  388.058168] CPU: 0 PID: 89 Comm: bash Not tainted 5.12.0-rc8-dirty #90
>>> [  388.058175] Hardware name: riscv-virtio,qemu (DT)
>>> [  388.058187] epc : number+0x32/0x2c0
>>> [  388.058247]  ra : vsnprintf+0x2ae/0x3f0
>>> [  388.058255] epc : ffffffe0002d38f6 ra : ffffffe0002d814e sp : ffffffd01425ffc0
>>> [  388.058263]  gp : ffffffe0012e4010 tp : ffffffe08014da00 t0 : ffffffd0142606e8
>>> [  388.058271]  t1 : 0000000000000000 t2 : 0000000000000000 s0 : ffffffd014260070
>>> [  388.058303]  s1 : ffffffd014260158 a0 : ffffffd01426015e a1 : ffffffd014260158
>>> [  388.058311]  a2 : 0000000000000013 a3 : ffff0a01ffffff10 a4 : ffffffe000c398e0
>>> [  388.058319]  a5 : 511b02ec65f3e300 a6 : 0000000000a1749a a7 : 0000000000000000
>>> [  388.058327]  s2 : ffffffff000000ff s3 : 00000000ffff0a01 s4 : ffffffe0012e50a8
>>> [  388.058335]  s5 : 0000000000ffff0a s6 : ffffffe0012e50a8 s7 : ffffffe000da1cc0
>>> [  388.058343]  s8 : ffffffffffffffff s9 : ffffffd0142602b0 s10: ffffffd0142602a8
>>> [  388.058351]  s11: ffffffd01426015e t3 : 00000000000f0000 t4 : ffffffffffffffff
>>> [  388.058359]  t5 : 000000000000002f t6 : ffffffd014260158
>>> [  388.058366] status: 0000000000000100 badaddr: ffffffd01425fff8 cause: 000000000000000f
>>> [  388.058374] Kernel panic - not syncing: Kernel stack overflow
>>> [  388.058381] CPU: 0 PID: 89 Comm: bash Not tainted 5.12.0-rc8-dirty #90
>>> [  388.058387] Hardware name: riscv-virtio,qemu (DT)
>>> [  388.058393] Call Trace:
>>> [  388.058400] [<ffffffe000004944>] walk_stackframe+0x0/0xce
>>> [  388.058406] [<ffffffe0006f0b28>] dump_backtrace+0x38/0x46
>>> [  388.058412] [<ffffffe0006f0b46>] show_stack+0x10/0x18
>>> [  388.058418] [<ffffffe0006f3690>] dump_stack+0x74/0x8e
>>> [  388.058424] [<ffffffe0006f0d52>] panic+0xfc/0x2b2
>>> [  388.058430] [<ffffffe0006f0acc>] print_trace_address+0x0/0x24
>>> [  388.058436] [<ffffffe0002d814e>] vsnprintf+0x2ae/0x3f0
>>> [  388.058956] SMP: stopping secondary CPUs
>>>
>>> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
>>> ---
>>> Change since rfc: fix rv32 and nommu defconfig compile error.
>>>
>>>   arch/riscv/Kconfig                   |   1 +
>>>   arch/riscv/include/asm/thread_info.h |  15 ++++
>>>   arch/riscv/kernel/entry.S            | 108 +++++++++++++++++++++++++++
>>>   arch/riscv/kernel/traps.c            |  35 +++++++++
>>>   4 files changed, 159 insertions(+)
>>>
>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>> index c426e7d20907..3e9c1945524d 100644
>>> --- a/arch/riscv/Kconfig
>>> +++ b/arch/riscv/Kconfig
>>> @@ -69,6 +69,7 @@ config RISCV
>>>   	select HAVE_ARCH_MMAP_RND_BITS if MMU
>>>   	select HAVE_ARCH_SECCOMP_FILTER
>>>   	select HAVE_ARCH_TRACEHOOK
>>> +	select HAVE_ARCH_VMAP_STACK if MMU && 64BIT
>>>   	select HAVE_ASM_MODVERSIONS
>>>   	select HAVE_CONTEXT_TRACKING
>>>   	select HAVE_DEBUG_KMEMLEAK
>>> diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
>>> index 0e549a3089b3..60da0dcacf14 100644
>>> --- a/arch/riscv/include/asm/thread_info.h
>>> +++ b/arch/riscv/include/asm/thread_info.h
>>> @@ -19,6 +19,21 @@
>>>   #endif
>>>   #define THREAD_SIZE		(PAGE_SIZE << THREAD_SIZE_ORDER)
>>>
>>> +/*
>>> + * By aligning VMAP'd stacks to 2 * THREAD_SIZE, we can detect overflow by
>>> + * checking sp & (1 << THREAD_SHIFT), which we can do cheaply in the entry
>>> + * assembly.
>>> + */
>>> +#ifdef CONFIG_VMAP_STACK
>>> +#define THREAD_ALIGN            (2 * THREAD_SIZE)
>>> +#else
>>> +#define THREAD_ALIGN            THREAD_SIZE
>>> +#endif
>>> +
>>> +#define THREAD_SHIFT            (PAGE_SHIFT + THREAD_SIZE_ORDER)
>>> +#define OVERFLOW_STACK_SIZE     SZ_4K
>>> +#define SHADOW_OVERFLOW_STACK_SIZE (1024)
>>> +
>>>   #ifndef __ASSEMBLY__
>>>
>>>   #include <asm/processor.h>
>>> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
>>> index 80d5a9e017b0..98f502654edd 100644
>>> --- a/arch/riscv/kernel/entry.S
>>> +++ b/arch/riscv/kernel/entry.S
>>> @@ -30,6 +30,15 @@ ENTRY(handle_exception)
>>>   _restore_kernel_tpsp:
>>>   	csrr tp, CSR_SCRATCH
>>>   	REG_S sp, TASK_TI_KERNEL_SP(tp)
>>> +
>>> +#ifdef CONFIG_VMAP_STACK
>>> +	addi sp, sp, -(PT_SIZE_ON_STACK)
>>> +	srli sp, sp, THREAD_SHIFT
>>> +	andi sp, sp, 0x1
>>> +	bnez sp, handle_kernel_stack_overflow
>>> +	REG_L sp, TASK_TI_KERNEL_SP(tp)
>>> +#endif
>>> +
>>>   _save_context:
>>>   	REG_S sp, TASK_TI_USER_SP(tp)
>>>   	REG_L sp, TASK_TI_KERNEL_SP(tp)
>>> @@ -376,6 +385,105 @@ handle_syscall_trace_exit:
>>>   	call do_syscall_trace_exit
>>>   	j ret_from_exception
>>>
>>> +#ifdef CONFIG_VMAP_STACK
>>> +handle_kernel_stack_overflow:
>>> +	la sp, shadow_stack
>>> +	addi sp, sp, SHADOW_OVERFLOW_STACK_SIZE
>>> +
>>> +	//save caller register to shadow stack
>>> +	addi sp, sp, -(PT_SIZE_ON_STACK)
>>> +	REG_S x1,  PT_RA(sp)
>>> +	REG_S x5,  PT_T0(sp)
>>> +	REG_S x6,  PT_T1(sp)
>>> +	REG_S x7,  PT_T2(sp)
>>> +	REG_S x10, PT_A0(sp)
>>> +	REG_S x11, PT_A1(sp)
>>> +	REG_S x12, PT_A2(sp)
>>> +	REG_S x13, PT_A3(sp)
>>> +	REG_S x14, PT_A4(sp)
>>> +	REG_S x15, PT_A5(sp)
>>> +	REG_S x16, PT_A6(sp)
>>> +	REG_S x17, PT_A7(sp)
>>> +	REG_S x28, PT_T3(sp)
>>> +	REG_S x29, PT_T4(sp)
>>> +	REG_S x30, PT_T5(sp)
>>> +	REG_S x31, PT_T6(sp)
>>> +
>>> +	la ra, restore_caller_reg
>>> +	tail get_overflow_stack
>>> +
>>> +restore_caller_reg:
>>> +	//save per-cpu overflow stack
>>> +	REG_S a0, -8(sp)
>>> +	//restore caller register from shadow_stack
>>> +	REG_L x1,  PT_RA(sp)
>>> +	REG_L x5,  PT_T0(sp)
>>> +	REG_L x6,  PT_T1(sp)
>>> +	REG_L x7,  PT_T2(sp)
>>> +	REG_L x10, PT_A0(sp)
>>> +	REG_L x11, PT_A1(sp)
>>> +	REG_L x12, PT_A2(sp)
>>> +	REG_L x13, PT_A3(sp)
>>> +	REG_L x14, PT_A4(sp)
>>> +	REG_L x15, PT_A5(sp)
>>> +	REG_L x16, PT_A6(sp)
>>> +	REG_L x17, PT_A7(sp)
>>> +	REG_L x28, PT_T3(sp)
>>> +	REG_L x29, PT_T4(sp)
>>> +	REG_L x30, PT_T5(sp)
>>> +	REG_L x31, PT_T6(sp)
>>> +
>>> +	//load per-cpu overflow stack
>>> +	REG_L sp, -8(sp)
>>> +	addi sp, sp, -(PT_SIZE_ON_STACK)
>>> +
>>> +	//save context to overflow stack
>>> +	REG_S x1,  PT_RA(sp)
>>> +	REG_S x3,  PT_GP(sp)
>>> +	REG_S x5,  PT_T0(sp)
>>> +	REG_S x6,  PT_T1(sp)
>>> +	REG_S x7,  PT_T2(sp)
>>> +	REG_S x8,  PT_S0(sp)
>>> +	REG_S x9,  PT_S1(sp)
>>> +	REG_S x10, PT_A0(sp)
>>> +	REG_S x11, PT_A1(sp)
>>> +	REG_S x12, PT_A2(sp)
>>> +	REG_S x13, PT_A3(sp)
>>> +	REG_S x14, PT_A4(sp)
>>> +	REG_S x15, PT_A5(sp)
>>> +	REG_S x16, PT_A6(sp)
>>> +	REG_S x17, PT_A7(sp)
>>> +	REG_S x18, PT_S2(sp)
>>> +	REG_S x19, PT_S3(sp)
>>> +	REG_S x20, PT_S4(sp)
>>> +	REG_S x21, PT_S5(sp)
>>> +	REG_S x22, PT_S6(sp)
>>> +	REG_S x23, PT_S7(sp)
>>> +	REG_S x24, PT_S8(sp)
>>> +	REG_S x25, PT_S9(sp)
>>> +	REG_S x26, PT_S10(sp)
>>> +	REG_S x27, PT_S11(sp)
>>> +	REG_S x28, PT_T3(sp)
>>> +	REG_S x29, PT_T4(sp)
>>> +	REG_S x30, PT_T5(sp)
>>> +	REG_S x31, PT_T6(sp)
>>> +
>>> +	REG_L s0, TASK_TI_KERNEL_SP(tp)
>>> +	csrr s1, CSR_STATUS
>>> +	csrr s2, CSR_EPC
>>> +	csrr s3, CSR_TVAL
>>> +	csrr s4, CSR_CAUSE
>>> +	csrr s5, CSR_SCRATCH
>>> +	REG_S s0, PT_SP(sp)
>>> +	REG_S s1, PT_STATUS(sp)
>>> +	REG_S s2, PT_EPC(sp)
>>> +	REG_S s3, PT_BADADDR(sp)
>>> +	REG_S s4, PT_CAUSE(sp)
>>> +	REG_S s5, PT_TP(sp)
>>> +	move a0, sp
>>> +	tail handle_bad_stack
>>> +#endif
>>> +
>>>   END(handle_exception)
>>>
>>>   ENTRY(ret_from_fork)
>>> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
>>> index 0721b9798595..3f7f618dab42 100644
>>> --- a/arch/riscv/kernel/traps.c
>>> +++ b/arch/riscv/kernel/traps.c
>>> @@ -198,3 +198,38 @@ int is_valid_bugaddr(unsigned long pc)
>>>   void __init trap_init(void)
>>>   {
>>>   }
>>> +
>>> +#ifdef CONFIG_VMAP_STACK
>>> +DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack)
>>> +		__aligned(16);
>>> +/*
>>> + * shadow stack, handled_ kernel_ stack_ overflow(in kernel/entry.S) is used
>>> + * to get per-cpu overflow stack(get_overflow_stack).
>>> + */
>>> +long shadow_stack[SHADOW_OVERFLOW_STACK_SIZE/sizeof(long)];
>>> +asmlinkage unsigned long get_overflow_stack(void)
>>> +{
>>> +	return (unsigned long)this_cpu_ptr(overflow_stack) +
>>> +		OVERFLOW_STACK_SIZE;
>>> +}
>>> +
>>> +asmlinkage void handle_bad_stack(struct pt_regs *regs)
>>> +{
>>> +	unsigned long tsk_stk = (unsigned long)current->stack;
>>> +	unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack);
>>> +
>>> +	console_verbose();
>>> +
>>> +	pr_emerg("Insufficient stack space to handle exception!\n");
>>> +	pr_emerg("Task stack:     [0x%016lx..0x%016lx]\n",
>>> +			tsk_stk, tsk_stk + THREAD_SIZE);
>>> +	pr_emerg("Overflow stack: [0x%016lx..0x%016lx]\n",
>>> +			ovf_stk, ovf_stk + OVERFLOW_STACK_SIZE);
>>> +
>>> +	__show_regs(regs);
>>> +	panic("Kernel stack overflow");
>>> +
>>> +	for (;;)
>>> +		wait_for_interrupt();
>>> +}
>>> +#endif