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@ -7,6 +7,7 @@
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#include <ucontext.h>
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#include <unistd.h>
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#include "arch_context.h"
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#include "software_interrupt.h"
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#define ARCH_SIG_JMP_OFF 8
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@ -31,7 +32,6 @@ struct arch_context {
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mcontext_t mctx;
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};
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extern void __attribute__((noreturn)) worker_thread_sandbox_switch_preempt(void);
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extern __thread struct arch_context worker_thread_base_context;
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static void __attribute__((noinline)) arch_context_init(struct arch_context *actx, reg_t ip, reg_t sp)
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@ -44,14 +44,15 @@ static void __attribute__((noinline)) arch_context_init(struct arch_context *act
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* context_switch conventions: bp is expected to be on top of the stack
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* when co-op context switching..
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*
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* so push sp on this new stack and use
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* that new sp as sp for switching to sandbox!
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* Temporarily switches the active stack to the stack pointer stored in sp
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* to push the stack pointer sp to the top of its own stack.
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* This acts as the base pointer
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*/
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asm volatile("movq %%rsp, %%rbx\n\t"
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"movq %%rax, %%rsp\n\t"
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"pushq %%rax\n\t"
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"movq %%rsp, %%rax\n\t"
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"movq %%rbx, %%rsp\n\t"
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asm volatile("movq %%rsp, %%rbx\n\t" /* Temporarily save pointer of active stack to B */
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"movq %%rax, %%rsp\n\t" /* Set active stack to stack pointer in A(C variable sp) */
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"pushq %%rax\n\t" /* Push A(C variable sp) onto the stack at sp */
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"movq %%rsp, %%rax\n\t" /* Write the incremented stack pointer to A(C variable sp) */
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"movq %%rbx, %%rsp\n\t" /* Restore original stack saved in B */
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: "=a"(sp)
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: "a"(sp)
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: "memory", "cc", "rbx");
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@ -122,6 +123,9 @@ arch_context_switch(struct arch_context *current, struct arch_context *next)
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/* if both current and next are NULL, there is no state change */
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assert(current != NULL || next != NULL);
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/* Assumption: The caller does not switch to itself */
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assert(current != next);
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/* Set any NULLs to worker_thread_base_context to resume execution of main */
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if (current == NULL) current = &worker_thread_base_context;
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if (next == NULL) next = &worker_thread_base_context;
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@ -129,27 +133,58 @@ arch_context_switch(struct arch_context *current, struct arch_context *next)
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reg_t *current_registers = current->regs, *next_registers = next->regs;
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assert(current_registers && next_registers);
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asm volatile("pushq %%rbp\n\t"
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"movq %%rsp, %%rbp\n\t"
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"movq $2f, 8(%%rax)\n\t"
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"movq %%rsp, (%%rax)\n\t"
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"cmpq $0, (%%rbx)\n\t"
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"je 1f\n\t"
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"movq (%%rbx), %%rsp\n\t"
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"jmpq *8(%%rbx)\n\t"
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"1:\n\t"
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"call worker_thread_sandbox_switch_preempt\n\t"
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".align 8\n\t"
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"2:\n\t"
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"movq $0, (%%rbx)\n\t"
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".align 8\n\t"
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"3:\n\t"
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"popq %%rbp\n\t"
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:
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: "a"(current_registers), "b"(next_registers)
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: "memory", "cc", "rcx", "rdx", "rsi", "rdi", "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15",
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"xmm0", "xmm1", "xmm2", "xmm3", "xmm4", "xmm5", "xmm6", "xmm7", "xmm8", "xmm9", "xmm10", "xmm11",
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"xmm12", "xmm13", "xmm14", "xmm15");
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asm volatile(
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/* Create a new stack frame */
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"pushq %%rbp\n\t" /* stack[stack_len++] = base_pointer */
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"movq %%rsp, %%rbp\n\t" /* base_pointer = stack_pointer. Start new Frame */
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/*
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* Save the IP and stack pointer to the context of the sandbox we're switching from
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*/
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"movq $2f, 8(%%rax)\n\t" /* Write the address of label 2 to current_registers[1] (instruction_pointer). */
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"movq %%rsp, (%%rax)\n\t" /* current_registers[0] (stack_pointer) = stack_pointer */
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/*
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* Check if the variant of the context we're trying to switch to is SLOW (mcontext-based)
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* If it is, jump to label 1 to restore the preempted sandbox
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*/
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"cmpq $0, (%%rbx)\n\t" /* if (stack pointer == 0) */
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"je 1f\n\t" /* goto 1; restore the existing sandbox using mcontext */
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/*
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* Fast Path
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* We can just write update the stack pointer and jump to the target instruction
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*/
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"movq (%%rbx), %%rsp\n\t" /* stack_pointer = next_registers[0] (stack_pointer) */
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"jmpq *8(%%rbx)\n\t" /* immediate jump to next_registers[1] (instruction_pointer) */
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/*
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* Slow Path
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* If the stack pointer equaled 0, that means the sandbox was preempted and we need to
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* fallback to a full mcontext-based context switch. We do this by invoking
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* arch_context_mcontext_restore, which fires a SIGUSR1 signal. The SIGUSR1 signal handler
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* executes the mcontext-based context switch.
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*/
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"1:\n\t"
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"call arch_context_mcontext_restore\n\t"
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".align 8\n\t"
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/*
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* Where preempted sandbox resumes
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* rbx contains the preempted sandbox's IP and SP in this context
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*/
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"2:\n\t"
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"movq $0, (%%rbx)\n\t" /* stack pointer = 0 */
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".align 8\n\t"
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/* This label is used in conjunction with a static offset */
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"3:\n\t"
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"popq %%rbp\n\t" /* base_pointer = stack[--stack_len]; Base Pointer is restored */
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:
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: "a"(current_registers), "b"(next_registers)
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: "memory", "cc", "rcx", "rdx", "rsi", "rdi", "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15", "xmm0",
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"xmm1", "xmm2", "xmm3", "xmm4", "xmm5", "xmm6", "xmm7", "xmm8", "xmm9", "xmm10", "xmm11", "xmm12", "xmm13",
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"xmm14", "xmm15");
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return 0;
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}
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Sean McBride
4 years ago
committed by
GitHub