Messages in this thread | | | Date | Thu, 24 Nov 2022 06:30:35 +0000 | From | Conor Dooley <> | Subject | Re: [PATCH] riscv: VMAP_STACK overflow detection thread-safe |
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Hey Deepak, Guo Ren s issues aside, there's some process bits here.
On 24 November 2022 00:50:06 GMT, Deepak Gupta <debug@rivosinc.com> wrote: >commit 31da94c25aea835ceac00575a9fd206c5a833fed added support for
Please check the documentation for how to format commit references in patch text. As a reader, a hash requires access to a git tree to do anything with. Id show you the format but I am on my phone ;)
>CONFIG_VMAP_STACK. If overflow is detected, CPU switches to `shadow_stack` >temporarily before switching finally to per-cpu `overflow_stack`. > >If two CPUs/harts are racing and end up in over flowing kernel stack, one >or both will end up corrupting each other state because `shadow_stack` is >not per-cpu. > >Following are the changes in this patch > > - Defines an asm macro to obtain per-cpu symbols in destination > register. > - Computing per-cpu symbol requires a temporary register. When stack is > out of question, a place is needed to spill a register. `thread_info` > is good location to have spill register. > - In entry.S when overflow is detected x31 is spilled into thread_info. > x31 is used as temp reg for asm macro to locate per-cpu overflow stack > >Other relevant disccussion on this >https://lore.kernel.org/linux-riscv/Y347B0x4VUNOd6V7@xhacker/T/#t
Link: foo
> >Tested by `echo EXHAUST_STACK > /sys/kernel/debug/provoke-crash/DIRECT` > >[ 286.223273] Insufficient stack space to handle exception!/debug/provoke-crash/DIRECT >[ 286.223878] Task stack: [0xff20000010a98000..0xff20000010a9c000] >[ 286.224411] Overflow stack: [0xff600001f7d98370..0xff600001f7d99370] >[ 286.226057] CPU: 1 PID: 205 Comm: bash Not tainted 6.1.0-rc2-00001-g328a1f96f7b9 #34 >[ 286.227139] Hardware name: riscv-virtio,qemu (DT) >[ 286.228000] epc : __memset+0x60/0xfc >[ 286.229299] ra : recursive_loop+0x48/0xc6 [lkdtm] >[ 286.231457] epc : ffffffff808de0e4 ra : ffffffff0163a752 sp : ff20000010a97e80 >[ 286.232207] gp : ffffffff815c0330 tp : ff600000820ea280 t0 : ff20000010a97e88 >[ 286.233584] t1 : 000000000000002e t2 : 3233206874706564 s0 : ff20000010a982b0 >[ 286.234293] s1 : 0000000000000012 a0 : ff20000010a97e88 a1 : 0000000000000000 >[ 286.234998] a2 : 0000000000000400 a3 : ff20000010a98288 a4 : 0000000000000000 >[ 286.235697] a5 : 0000000000000000 a6 : fffffffffffe43f0 a7 : 00007fffffffffff >[ 286.236384] s2 : ff20000010a97e88 s3 : ffffffff01644680 s4 : ff20000010a9be90 >[ 286.237743] s5 : ff600000842ba6c0 s6 : 00aaaaaac29e42b0 s7 : 00fffffff0aa3684 >[ 286.238691] s8 : 00aaaaaac2978040 s9 : 0000000000000065 s10: 00ffffff8a7cad10 >[ 286.239591] s11: 00ffffff8a76a4e0 t3 : ffffffff815dbaf4 t4 : ffffffff815dbaf4 >[ 286.240537] t5 : ffffffff815dbab8 t6 : ff20000010a9bb48 >[ 286.241540] status: 0000000200000120 badaddr: ff20000010a97e88 cause: 000000000000000f >[ 286.242979] Kernel panic - not syncing: Kernel stack overflow >[ 286.244106] CPU: 1 PID: 205 Comm: bash Not tainted 6.1.0-rc2-00001-g328a1f96f7b9 #34 >[ 286.245276] Hardware name: riscv-virtio,qemu (DT) >[ 286.245929] Call Trace: >[ 286.246954] [<ffffffff80006754>] dump_backtrace+0x30/0x38 >[ 286.247813] [<ffffffff808de798>] show_stack+0x40/0x4c >[ 286.248429] [<ffffffff808ea2a8>] dump_stack_lvl+0x44/0x5c >[ 286.249439] [<ffffffff808ea2d8>] dump_stack+0x18/0x20 >[ 286.250056] [<ffffffff808dec06>] panic+0x126/0x2fe >[ 286.250642] [<ffffffff800065ea>] walk_stackframe+0x0/0xf0 >[ 286.251357] [<ffffffff0163a752>] recursive_loop+0x48/0xc6 [lkdtm] >[ 286.253321] SMP: stopping secondary CPUs >[ 286.256724] ---[ end Kernel panic - not syncing: Kernel stack overflow ]---
For stack traces, especially long ones, please cut out the timestamps.
>Fixes: 31da94c25aea835ceac00575a9fd206c5a833fed
https://gist.githubusercontent.com/conor-pwbot/8882fc7ef7cd4fe833774574fbf509f5/raw/d360ec7aebfaa6c2d043e9bd87f59745ad6a4c85/desc
Please use the correct format for fixes tags.
>Cc: Guo Ren <guoren@kernel.org> >Cc: Jisheng Zhang <jszhang@kernel.org> > >Signed-off-by: Deepak Gupta <debug@rivosinc.com>
All of the tags need to be in one block, so:
Link: Fixes: SoB:
Thanks, Conor.
>--- > arch/riscv/include/asm/asm.h | 11 ++++++ > arch/riscv/include/asm/thread_info.h | 3 ++ > arch/riscv/kernel/asm-offsets.c | 4 +++ > arch/riscv/kernel/entry.S | 54 ++++------------------------ > arch/riscv/kernel/traps.c | 12 +------ > 5 files changed, 26 insertions(+), 58 deletions(-) > >diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h >index 1b471ff73178..373eba843331 100644 >--- a/arch/riscv/include/asm/asm.h >+++ b/arch/riscv/include/asm/asm.h >@@ -69,6 +69,7 @@ > > #ifdef __ASSEMBLY__ > >+#include <asm/asm-offsets.h> > /* Common assembly source macros */ > > /* >@@ -80,6 +81,16 @@ > .endr > .endm > >+.macro asm_per_cpu dst sym tmp >+ REG_L \tmp, TASK_TI_CPU_NUM(tp) >+ slli \tmp, \tmp, 0x3 >+ la \dst, __per_cpu_offset >+ add \dst, \dst, \tmp >+ REG_L \tmp, 0(\dst) >+ la \dst, \sym >+ add \dst, \dst, \tmp >+.endm >+ > #endif /* __ASSEMBLY__ */ > > #endif /* _ASM_RISCV_ASM_H */ >diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h >index 67322f878e0d..7e17dc07cf11 100644 >--- a/arch/riscv/include/asm/thread_info.h >+++ b/arch/riscv/include/asm/thread_info.h >@@ -65,6 +65,9 @@ struct thread_info { > */ > long kernel_sp; /* Kernel stack pointer */ > long user_sp; /* User stack pointer */ >+#ifdef CONFIG_VMAP_STACK >+ long spill_reg; /* per cpu scratch space to spill a single register */ >+#endif > int cpu; > }; > >diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c >index df9444397908..bed3c83bfb8f 100644 >--- a/arch/riscv/kernel/asm-offsets.c >+++ b/arch/riscv/kernel/asm-offsets.c >@@ -38,6 +38,10 @@ void asm_offsets(void) > OFFSET(TASK_TI_KERNEL_SP, task_struct, thread_info.kernel_sp); > OFFSET(TASK_TI_USER_SP, task_struct, thread_info.user_sp); > >+ OFFSET(TASK_TI_CPU_NUM, task_struct, thread_info.cpu); >+#ifdef CONFIG_VMAP_STACK >+ OFFSET(TASK_TI_SPILL_REG, task_struct, thread_info.spill_reg); >+#endif > OFFSET(TASK_THREAD_F0, task_struct, thread.fstate.f[0]); > OFFSET(TASK_THREAD_F1, task_struct, thread.fstate.f[1]); > OFFSET(TASK_THREAD_F2, task_struct, thread.fstate.f[2]); >diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S >index b9eda3fcbd6d..12f285cec136 100644 >--- a/arch/riscv/kernel/entry.S >+++ b/arch/riscv/kernel/entry.S >@@ -10,9 +10,11 @@ > #include <asm/asm.h> > #include <asm/csr.h> > #include <asm/unistd.h> >+#include <asm/page.h> > #include <asm/thread_info.h> > #include <asm/asm-offsets.h> > #include <asm/errata_list.h> >+#include <linux/sizes.h> > > #if !IS_ENABLED(CONFIG_PREEMPTION) > .set resume_kernel, restore_all >@@ -404,54 +406,12 @@ handle_syscall_trace_exit: > > #ifdef CONFIG_VMAP_STACK > handle_kernel_stack_overflow: >- la sp, shadow_stack >- addi sp, sp, SHADOW_OVERFLOW_STACK_SIZE >+ REG_S x31, TASK_TI_SPILL_REG(tp) >+ asm_per_cpu sp, overflow_stack, x31 >+ li x31, OVERFLOW_STACK_SIZE >+ add sp, sp, x31 >+ REG_L x31, TASK_TI_SPILL_REG(tp) > >- //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 >diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c >index f3e96d60a2ff..eef3a87514c7 100644 >--- a/arch/riscv/kernel/traps.c >+++ b/arch/riscv/kernel/traps.c >@@ -208,18 +208,8 @@ int is_valid_bugaddr(unsigned long pc) > #endif /* CONFIG_GENERIC_BUG */ > > #ifdef CONFIG_VMAP_STACK >-static DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], >+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) > {
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