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Diffstat (limited to 'drivers/lguest/x86/core.c')
| -rw-r--r-- | drivers/lguest/x86/core.c | 596 |
1 files changed, 596 insertions, 0 deletions
diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c new file mode 100644 index 0000000..bf79423 --- /dev/null +++ b/drivers/lguest/x86/core.c @@ -0,0 +1,596 @@ +/* + * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation. + * Copyright (C) 2007, Jes Sorensen <jes@sgi.com> SGI. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or + * NON INFRINGEMENT. See the GNU General Public License for more + * details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ +/*P:450 This file contains the x86-specific lguest code. It used to be all + * mixed in with drivers/lguest/core.c but several foolhardy code slashers + * wrestled most of the dependencies out to here in preparation for porting + * lguest to other architectures (see what I mean by foolhardy?). + * + * This also contains a couple of non-obvious setup and teardown pieces which + * were implemented after days of debugging pain. :*/ +#include <linux/kernel.h> +#include <linux/start_kernel.h> +#include <linux/string.h> +#include <linux/console.h> +#include <linux/screen_info.h> +#include <linux/irq.h> +#include <linux/interrupt.h> +#include <linux/clocksource.h> +#include <linux/clockchips.h> +#include <linux/cpu.h> +#include <linux/lguest.h> +#include <linux/lguest_launcher.h> +#include <asm/paravirt.h> +#include <asm/param.h> +#include <asm/page.h> +#include <asm/pgtable.h> +#include <asm/desc.h> +#include <asm/setup.h> +#include <asm/lguest.h> +#include <asm/uaccess.h> +#include <asm/i387.h> +#include "../lg.h" + +static int cpu_had_pge; + +static struct { + unsigned long offset; + unsigned short segment; +} lguest_entry; + +/* Offset from where switcher.S was compiled to where we've copied it */ +static unsigned long switcher_offset(void) +{ + return SWITCHER_ADDR - (unsigned long)start_switcher_text; +} + +/* This cpu's struct lguest_pages. */ +static struct lguest_pages *lguest_pages(unsigned int cpu) +{ + return &(((struct lguest_pages *) + (SWITCHER_ADDR + SHARED_SWITCHER_PAGES*PAGE_SIZE))[cpu]); +} + +static DEFINE_PER_CPU(struct lg_cpu *, last_cpu); + +/*S:010 + * We approach the Switcher. + * + * Remember that each CPU has two pages which are visible to the Guest when it + * runs on that CPU. This has to contain the state for that Guest: we copy the + * state in just before we run the Guest. + * + * Each Guest has "changed" flags which indicate what has changed in the Guest + * since it last ran. We saw this set in interrupts_and_traps.c and + * segments.c. + */ +static void copy_in_guest_info(struct lg_cpu *cpu, struct lguest_pages *pages) +{ + /* Copying all this data can be quite expensive. We usually run the + * same Guest we ran last time (and that Guest hasn't run anywhere else + * meanwhile). If that's not the case, we pretend everything in the + * Guest has changed. */ + if (__get_cpu_var(last_cpu) != cpu || cpu->last_pages != pages) { + __get_cpu_var(last_cpu) = cpu; + cpu->last_pages = pages; + cpu->changed = CHANGED_ALL; + } + + /* These copies are pretty cheap, so we do them unconditionally: */ + /* Save the current Host top-level page directory. */ + pages->state.host_cr3 = __pa(current->mm->pgd); + /* Set up the Guest's page tables to see this CPU's pages (and no + * other CPU's pages). */ + map_switcher_in_guest(cpu, pages); + /* Set up the two "TSS" members which tell the CPU what stack to use + * for traps which do directly into the Guest (ie. traps at privilege + * level 1). */ + pages->state.guest_tss.sp1 = cpu->esp1; + pages->state.guest_tss.ss1 = cpu->ss1; + + /* Copy direct-to-Guest trap entries. */ + if (cpu->changed & CHANGED_IDT) + copy_traps(cpu, pages->state.guest_idt, default_idt_entries); + + /* Copy all GDT entries which the Guest can change. */ + if (cpu->changed & CHANGED_GDT) + copy_gdt(cpu, pages->state.guest_gdt); + /* If only the TLS entries have changed, copy them. */ + else if (cpu->changed & CHANGED_GDT_TLS) + copy_gdt_tls(cpu, pages->state.guest_gdt); + + /* Mark the Guest as unchanged for next time. */ + cpu->changed = 0; +} + +/* Finally: the code to actually call into the Switcher to run the Guest. */ +static void run_guest_once(struct lg_cpu *cpu, struct lguest_pages *pages) +{ + /* This is a dummy value we need for GCC's sake. */ + unsigned int clobber; + + /* Copy the guest-specific information into this CPU's "struct + * lguest_pages". */ + copy_in_guest_info(cpu, pages); + + /* Set the trap number to 256 (impossible value). If we fault while + * switching to the Guest (bad segment registers or bug), this will + * cause us to abort the Guest. */ + cpu->regs->trapnum = 256; + + /* Now: we push the "eflags" register on the stack, then do an "lcall". + * This is how we change from using the kernel code segment to using + * the dedicated lguest code segment, as well as jumping into the + * Switcher. + * + * The lcall also pushes the old code segment (KERNEL_CS) onto the + * stack, then the address of this call. This stack layout happens to + * exactly match the stack layout created by an interrupt... */ + asm volatile("pushf; lcall *lguest_entry" + /* This is how we tell GCC that %eax ("a") and %ebx ("b") + * are changed by this routine. The "=" means output. */ + : "=a"(clobber), "=b"(clobber) + /* %eax contains the pages pointer. ("0" refers to the + * 0-th argument above, ie "a"). %ebx contains the + * physical address of the Guest's top-level page + * directory. */ + : "0"(pages), "1"(__pa(cpu->lg->pgdirs[cpu->cpu_pgd].pgdir)) + /* We tell gcc that all these registers could change, + * which means we don't have to save and restore them in + * the Switcher. */ + : "memory", "%edx", "%ecx", "%edi", "%esi"); +} +/*:*/ + +/*M:002 There are hooks in the scheduler which we can register to tell when we + * get kicked off the CPU (preempt_notifier_register()). This would allow us + * to lazily disable SYSENTER which would regain some performance, and should + * also simplify copy_in_guest_info(). Note that we'd still need to restore + * things when we exit to Launcher userspace, but that's fairly easy. + * + * We could also try using this hooks for PGE, but that might be too expensive. + * + * The hooks were designed for KVM, but we can also put them to good use. :*/ + +/*H:040 This is the i386-specific code to setup and run the Guest. Interrupts + * are disabled: we own the CPU. */ +void lguest_arch_run_guest(struct lg_cpu *cpu) +{ + /* Remember the awfully-named TS bit? If the Guest has asked to set it + * we set it now, so we can trap and pass that trap to the Guest if it + * uses the FPU. */ + if (cpu->ts) + unlazy_fpu(current); + + /* SYSENTER is an optimized way of doing system calls. We can't allow + * it because it always jumps to privilege level 0. A normal Guest + * won't try it because we don't advertise it in CPUID, but a malicious + * Guest (or malicious Guest userspace program) could, so we tell the + * CPU to disable it before running the Guest. */ + if (boot_cpu_has(X86_FEATURE_SEP)) + wrmsr(MSR_IA32_SYSENTER_CS, 0, 0); + + /* Now we actually run the Guest. It will return when something + * interesting happens, and we can examine its registers to see what it + * was doing. */ + run_guest_once(cpu, lguest_pages(raw_smp_processor_id())); + + /* Note that the "regs" structure contains two extra entries which are + * not really registers: a trap number which says what interrupt or + * trap made the switcher code come back, and an error code which some + * traps set. */ + + /* Restore SYSENTER if it's supposed to be on. */ + if (boot_cpu_has(X86_FEATURE_SEP)) + wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0); + + /* If the Guest page faulted, then the cr2 register will tell us the + * bad virtual address. We have to grab this now, because once we + * re-enable interrupts an interrupt could fault and thus overwrite + * cr2, or we could even move off to a different CPU. */ + if (cpu->regs->trapnum == 14) + cpu->arch.last_pagefault = read_cr2(); + /* Similarly, if we took a trap because the Guest used the FPU, + * we have to restore the FPU it expects to see. + * math_state_restore() may sleep and we may even move off to + * a different CPU. So all the critical stuff should be done + * before this. */ + else if (cpu->regs->trapnum == 7) + math_state_restore(); +} + +/*H:130 Now we've examined the hypercall code; our Guest can make requests. + * Our Guest is usually so well behaved; it never tries to do things it isn't + * allowed to, and uses hypercalls instead. Unfortunately, Linux's paravirtual + * infrastructure isn't quite complete, because it doesn't contain replacements + * for the Intel I/O instructions. As a result, the Guest sometimes fumbles + * across one during the boot process as it probes for various things which are + * usually attached to a PC. + * + * When the Guest uses one of these instructions, we get a trap (General + * Protection Fault) and come here. We see if it's one of those troublesome + * instructions and skip over it. We return true if we did. */ +static int emulate_insn(struct lg_cpu *cpu) +{ + u8 insn; + unsigned int insnlen = 0, in = 0, shift = 0; + /* The eip contains the *virtual* address of the Guest's instruction: + * guest_pa just subtracts the Guest's page_offset. */ + unsigned long physaddr = guest_pa(cpu, cpu->regs->eip); + + /* This must be the Guest kernel trying to do something, not userspace! + * The bottom two bits of the CS segment register are the privilege + * level. */ + if ((cpu->regs->cs & 3) != GUEST_PL) + return 0; + + /* Decoding x86 instructions is icky. */ + insn = lgread(cpu, physaddr, u8); + + /* 0x66 is an "operand prefix". It means it's using the upper 16 bits + of the eax register. */ + if (insn == 0x66) { + shift = 16; + /* The instruction is 1 byte so far, read the next byte. */ + insnlen = 1; + insn = lgread(cpu, physaddr + insnlen, u8); + } + + /* We can ignore the lower bit for the moment and decode the 4 opcodes + * we need to emulate. */ + switch (insn & 0xFE) { + case 0xE4: /* in <next byte>,%al */ + insnlen += 2; + in = 1; + break; + case 0xEC: /* in (%dx),%al */ + insnlen += 1; + in = 1; + break; + case 0xE6: /* out %al,<next byte> */ + insnlen += 2; + break; + case 0xEE: /* out %al,(%dx) */ + insnlen += 1; + break; + default: + /* OK, we don't know what this is, can't emulate. */ + return 0; + } + + /* If it was an "IN" instruction, they expect the result to be read + * into %eax, so we change %eax. We always return all-ones, which + * traditionally means "there's nothing there". */ + if (in) { + /* Lower bit tells is whether it's a 16 or 32 bit access */ + if (insn & 0x1) + cpu->regs->eax = 0xFFFFFFFF; + else + cpu->regs->eax |= (0xFFFF << shift); + } + /* Finally, we've "done" the instruction, so move past it. */ + cpu->regs->eip += insnlen; + /* Success! */ + return 1; +} + +/*H:050 Once we've re-enabled interrupts, we look at why the Guest exited. */ +void lguest_arch_handle_trap(struct lg_cpu *cpu) +{ + switch (cpu->regs->trapnum) { + case 13: /* We've intercepted a General Protection Fault. */ + /* Check if this was one of those annoying IN or OUT + * instructions which we need to emulate. If so, we just go + * back into the Guest after we've done it. */ + if (cpu->regs->errcode == 0) { + if (emulate_insn(cpu)) + return; + } + break; + case 14: /* We've intercepted a Page Fault. */ + /* The Guest accessed a virtual address that wasn't mapped. + * This happens a lot: we don't actually set up most of the page + * tables for the Guest at all when we start: as it runs it asks + * for more and more, and we set them up as required. In this + * case, we don't even tell the Guest that the fault happened. + * + * The errcode tells whether this was a read or a write, and + * whether kernel or userspace code. */ + if (demand_page(cpu, cpu->arch.last_pagefault, + cpu->regs->errcode)) + return; + + /* OK, it's really not there (or not OK): the Guest needs to + * know. We write out the cr2 value so it knows where the + * fault occurred. + * + * Note that if the Guest were really messed up, this could + * happen before it's done the LHCALL_LGUEST_INIT hypercall, so + * lg->lguest_data could be NULL */ + if (cpu->lg->lguest_data && + put_user(cpu->arch.last_pagefault, + &cpu->lg->lguest_data->cr2)) + kill_guest(cpu, "Writing cr2"); + break; + case 7: /* We've intercepted a Device Not Available fault. */ + /* If the Guest doesn't want to know, we already restored the + * Floating Point Unit, so we just continue without telling + * it. */ + if (!cpu->ts) + return; + break; + case 32 ... 255: + /* These values mean a real interrupt occurred, in which case + * the Host handler has already been run. We just do a + * friendly check if another process should now be run, then + * return to run the Guest again */ + cond_resched(); + return; + case LGUEST_TRAP_ENTRY: + /* Our 'struct hcall_args' maps directly over our regs: we set + * up the pointer now to indicate a hypercall is pending. */ + cpu->hcall = (struct hcall_args *)cpu->regs; + return; + } + + /* We didn't handle the trap, so it needs to go to the Guest. */ + if (!deliver_trap(cpu, cpu->regs->trapnum)) + /* If the Guest doesn't have a handler (either it hasn't + * registered any yet, or it's one of the faults we don't let + * it handle), it dies with this cryptic error message. */ + kill_guest(cpu, "unhandled trap %li at %#lx (%#lx)", + cpu->regs->trapnum, cpu->regs->eip, + cpu->regs->trapnum == 14 ? cpu->arch.last_pagefault + : cpu->regs->errcode); +} + +/* Now we can look at each of the routines this calls, in increasing order of + * complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(), + * deliver_trap() and demand_page(). After all those, we'll be ready to + * examine the Switcher, and our philosophical understanding of the Host/Guest + * duality will be complete. :*/ +static void adjust_pge(void *on) +{ + if (on) + write_cr4(read_cr4() | X86_CR4_PGE); + else + write_cr4(read_cr4() & ~X86_CR4_PGE); +} + +/*H:020 Now the Switcher is mapped and every thing else is ready, we need to do + * some more i386-specific initialization. */ +void __init lguest_arch_host_init(void) +{ + int i; + + /* Most of the i386/switcher.S doesn't care that it's been moved; on + * Intel, jumps are relative, and it doesn't access any references to + * external code or data. + * + * The only exception is the interrupt handlers in switcher.S: their + * addresses are placed in a table (default_idt_entries), so we need to + * update the table with the new addresses. switcher_offset() is a + * convenience function which returns the distance between the + * compiled-in switcher code and the high-mapped copy we just made. */ + for (i = 0; i < IDT_ENTRIES; i++) + default_idt_entries[i] += switcher_offset(); + + /* + * Set up the Switcher's per-cpu areas. + * + * Each CPU gets two pages of its own within the high-mapped region + * (aka. "struct lguest_pages"). Much of this can be initialized now, + * but some depends on what Guest we are running (which is set up in + * copy_in_guest_info()). + */ + for_each_possible_cpu(i) { + /* lguest_pages() returns this CPU's two pages. */ + struct lguest_pages *pages = lguest_pages(i); + /* This is a convenience pointer to make the code fit one + * statement to a line. */ + struct lguest_ro_state *state = &pages->state; + + /* The Global Descriptor Table: the Host has a different one + * for each CPU. We keep a descriptor for the GDT which says + * where it is and how big it is (the size is actually the last + * byte, not the size, hence the "-1"). */ + state->host_gdt_desc.size = GDT_SIZE-1; + state->host_gdt_desc.address = (long)get_cpu_gdt_table(i); + + /* All CPUs on the Host use the same Interrupt Descriptor + * Table, so we just use store_idt(), which gets this CPU's IDT + * descriptor. */ + store_idt(&state->host_idt_desc); + + /* The descriptors for the Guest's GDT and IDT can be filled + * out now, too. We copy the GDT & IDT into ->guest_gdt and + * ->guest_idt before actually running the Guest. */ + state->guest_idt_desc.size = sizeof(state->guest_idt)-1; + state->guest_idt_desc.address = (long)&state->guest_idt; + state->guest_gdt_desc.size = sizeof(state->guest_gdt)-1; + state->guest_gdt_desc.address = (long)&state->guest_gdt; + + /* We know where we want the stack to be when the Guest enters + * the Switcher: in pages->regs. The stack grows upwards, so + * we start it at the end of that structure. */ + state->guest_tss.sp0 = (long)(&pages->regs + 1); + /* And this is the GDT entry to use for the stack: we keep a + * couple of special LGUEST entries. */ + state->guest_tss.ss0 = LGUEST_DS; + + /* x86 can have a finegrained bitmap which indicates what I/O + * ports the process can use. We set it to the end of our + * structure, meaning "none". */ + state->guest_tss.io_bitmap_base = sizeof(state->guest_tss); + + /* Some GDT entries are the same across all Guests, so we can + * set them up now. */ + setup_default_gdt_entries(state); + /* Most IDT entries are the same for all Guests, too.*/ + setup_default_idt_entries(state, default_idt_entries); + + /* The Host needs to be able to use the LGUEST segments on this + * CPU, too, so put them in the Host GDT. */ + get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT; + get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT; + } + + /* In the Switcher, we want the %cs segment register to use the + * LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so + * it will be undisturbed when we switch. To change %cs and jump we + * need this structure to feed to Intel's "lcall" instruction. */ + lguest_entry.offset = (long)switch_to_guest + switcher_offset(); + lguest_entry.segment = LGUEST_CS; + + /* Finally, we need to turn off "Page Global Enable". PGE is an + * optimization where page table entries are specially marked to show + * they never change. The Host kernel marks all the kernel pages this + * way because it's always present, even when userspace is running. + * + * Lguest breaks this: unbeknownst to the rest of the Host kernel, we + * switch to the Guest kernel. If you don't disable this on all CPUs, + * you'll get really weird bugs that you'll chase for two days. + * + * I used to turn PGE off every time we switched to the Guest and back + * on when we return, but that slowed the Switcher down noticibly. */ + + /* We don't need the complexity of CPUs coming and going while we're + * doing this. */ + get_online_cpus(); + if (cpu_has_pge) { /* We have a broader idea of "global". */ + /* Remember that this was originally set (for cleanup). */ + cpu_had_pge = 1; + /* adjust_pge is a helper function which sets or unsets the PGE + * bit on its CPU, depending on the argument (0 == unset). */ + on_each_cpu(adjust_pge, (void *)0, 1); + /* Turn off the feature in the global feature set. */ + clear_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE); + } + put_online_cpus(); +}; +/*:*/ + +void __exit lguest_arch_host_fini(void) +{ + /* If we had PGE before we started, turn it back on now. */ + get_online_cpus(); + if (cpu_had_pge) { + set_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE); + /* adjust_pge's argument "1" means set PGE. */ + on_each_cpu(adjust_pge, (void *)1, 1); + } + put_online_cpus(); +} + + +/*H:122 The i386-specific hypercalls simply farm out to the right functions. */ +int lguest_arch_do_hcall(struct lg_cpu *cpu, struct hcall_args *args) +{ + switch (args->arg0) { + case LHCALL_LOAD_GDT: + load_guest_gdt(cpu, args->arg1, args->arg2); + break; + case LHCALL_LOAD_IDT_ENTRY: + load_guest_idt_entry(cpu, args->arg1, args->arg2, args->arg3); + break; + case LHCALL_LOAD_TLS: + guest_load_tls(cpu, args->arg1); + break; + default: + /* Bad Guest. Bad! */ + return -EIO; + } + return 0; +} + +/*H:126 i386-specific hypercall initialization: */ +int lguest_arch_init_hypercalls(struct lg_cpu *cpu) +{ + u32 tsc_speed; + + /* The pointer to the Guest's "struct lguest_data" is the only argument. + * We check that address now. */ + if (!lguest_address_ok(cpu->lg, cpu->hcall->arg1, + sizeof(*cpu->lg->lguest_data))) + return -EFAULT; + + /* Having checked it, we simply set lg->lguest_data to point straight + * into the Launcher's memory at the right place and then use + * copy_to_user/from_user from now on, instead of lgread/write. I put + * this in to show that I'm not immune to writing stupid + * optimizations. */ + cpu->lg->lguest_data = cpu->lg->mem_base + cpu->hcall->arg1; + + /* We insist that the Time Stamp Counter exist and doesn't change with + * cpu frequency. Some devious chip manufacturers decided that TSC + * changes could be handled in software. I decided that time going + * backwards might be good for benchmarks, but it's bad for users. + * + * We also insist that the TSC be stable: the kernel detects unreliable + * TSCs for its own purposes, and we use that here. */ + if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && !check_tsc_unstable()) + tsc_speed = tsc_khz; + else + tsc_speed = 0; + if (put_user(tsc_speed, &cpu->lg->lguest_data->tsc_khz)) + return -EFAULT; + + /* The interrupt code might not like the system call vector. */ + if (!check_syscall_vector(cpu->lg)) + kill_guest(cpu, "bad syscall vector"); + + return 0; +} +/*:*/ + +/*L:030 lguest_arch_setup_regs() + * + * Most of the Guest's registers are left alone: we used get_zeroed_page() to + * allocate the structure, so they will be 0. */ +void lguest_arch_setup_regs(struct lg_cpu *cpu, unsigned long start) +{ + struct lguest_regs *regs = cpu->regs; + + /* There are four "segment" registers which the Guest needs to boot: + * The "code segment" register (cs) refers to the kernel code segment + * __KERNEL_CS, and the "data", "extra" and "stack" segment registers + * refer to the kernel data segment __KERNEL_DS. + * + * The privilege level is packed into the lower bits. The Guest runs + * at privilege level 1 (GUEST_PL).*/ + regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL; + regs->cs = __KERNEL_CS|GUEST_PL; + + /* The "eflags" register contains miscellaneous flags. Bit 1 (0x002) + * is supposed to always be "1". Bit 9 (0x200) controls whether + * interrupts are enabled. We always leave interrupts enabled while + * running the Guest. */ + regs->eflags = X86_EFLAGS_IF | 0x2; + + /* The "Extended Instruction Pointer" register says where the Guest is + * running. */ + regs->eip = start; + + /* %esi points to our boot information, at physical address 0, so don't + * touch it. */ + + /* There are a couple of GDT entries the Guest expects when first + * booting. */ + setup_guest_gdt(cpu); +} |
