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Allow guest to specify syscall vector to use.
(Based on Ron Minnich's LGUEST_PLAN9_SYSCALL patch). This patch allows Guests to specify what system call vector they want, and we try to reserve it. We only allow one non-Linux system call vector, to try to avoid DoS on the Host. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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@ -87,6 +87,7 @@ struct lguest_data lguest_data = {
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.noirq_start = (u32)lguest_noirq_start,
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.noirq_end = (u32)lguest_noirq_end,
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.blocked_interrupts = { 1 }, /* Block timer interrupts */
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.syscall_vec = SYSCALL_VECTOR,
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};
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static cycle_t clock_base;
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@ -281,37 +281,47 @@ static int __init init(void)
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/* First we put the Switcher up in very high virtual memory. */
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err = map_switcher();
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if (err)
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return err;
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goto out;
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/* Now we set up the pagetable implementation for the Guests. */
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err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
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if (err) {
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unmap_switcher();
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return err;
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}
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if (err)
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goto unmap;
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/* The I/O subsystem needs some things initialized. */
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lguest_io_init();
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/* We might need to reserve an interrupt vector. */
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err = init_interrupts();
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if (err)
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goto free_pgtables;
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/* /dev/lguest needs to be registered. */
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err = lguest_device_init();
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if (err) {
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free_pagetables();
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unmap_switcher();
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return err;
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}
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if (err)
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goto free_interrupts;
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/* Finally we do some architecture-specific setup. */
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lguest_arch_host_init();
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/* All good! */
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return 0;
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free_interrupts:
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free_interrupts();
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free_pgtables:
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free_pagetables();
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unmap:
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unmap_switcher();
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out:
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return err;
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}
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/* Cleaning up is just the same code, backwards. With a little French. */
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static void __exit fini(void)
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{
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lguest_device_remove();
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free_interrupts();
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free_pagetables();
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unmap_switcher();
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@ -12,8 +12,14 @@
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* them first, so we also have a way of "reflecting" them into the Guest as if
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* they had been delivered to it directly. :*/
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#include <linux/uaccess.h>
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#include <linux/interrupt.h>
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#include <linux/module.h>
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#include "lg.h"
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/* Allow Guests to use a non-128 (ie. non-Linux) syscall trap. */
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static unsigned int syscall_vector = SYSCALL_VECTOR;
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module_param(syscall_vector, uint, 0444);
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/* The address of the interrupt handler is split into two bits: */
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static unsigned long idt_address(u32 lo, u32 hi)
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{
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@ -183,6 +189,47 @@ void maybe_do_interrupt(struct lguest *lg)
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* timer interrupt. */
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write_timestamp(lg);
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}
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/*:*/
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/* Linux uses trap 128 for system calls. Plan9 uses 64, and Ron Minnich sent
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* me a patch, so we support that too. It'd be a big step for lguest if half
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* the Plan 9 user base were to start using it.
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*
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* Actually now I think of it, it's possible that Ron *is* half the Plan 9
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* userbase. Oh well. */
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static bool could_be_syscall(unsigned int num)
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{
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/* Normal Linux SYSCALL_VECTOR or reserved vector? */
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return num == SYSCALL_VECTOR || num == syscall_vector;
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}
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/* The syscall vector it wants must be unused by Host. */
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bool check_syscall_vector(struct lguest *lg)
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{
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u32 vector;
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if (get_user(vector, &lg->lguest_data->syscall_vec))
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return false;
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return could_be_syscall(vector);
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}
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int init_interrupts(void)
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{
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/* If they want some strange system call vector, reserve it now */
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if (syscall_vector != SYSCALL_VECTOR
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&& test_and_set_bit(syscall_vector, used_vectors)) {
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printk("lg: couldn't reserve syscall %u\n", syscall_vector);
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return -EBUSY;
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}
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return 0;
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}
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void free_interrupts(void)
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{
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if (syscall_vector != SYSCALL_VECTOR)
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clear_bit(syscall_vector, used_vectors);
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}
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/*H:220 Now we've got the routines to deliver interrupts, delivering traps
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* like page fault is easy. The only trick is that Intel decided that some
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@ -224,7 +271,7 @@ static int direct_trap(unsigned int num)
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{
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/* Hardware interrupts don't go to the Guest at all (except system
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* call). */
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if (num >= FIRST_EXTERNAL_VECTOR && num != SYSCALL_VECTOR)
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if (num >= FIRST_EXTERNAL_VECTOR && !could_be_syscall(num))
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return 0;
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/* The Host needs to see page faults (for shadow paging and to save the
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@ -141,6 +141,9 @@ void copy_traps(const struct lguest *lg, struct desc_struct *idt,
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const unsigned long *def);
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void guest_set_clockevent(struct lguest *lg, unsigned long delta);
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void init_clockdev(struct lguest *lg);
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bool check_syscall_vector(struct lguest *lg);
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int init_interrupts(void);
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void free_interrupts(void);
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/* segments.c: */
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void setup_default_gdt_entries(struct lguest_ro_state *state);
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@ -530,6 +530,10 @@ int lguest_arch_init_hypercalls(struct lguest *lg)
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if (put_user(tsc_speed, &lg->lguest_data->tsc_khz))
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return -EFAULT;
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/* The interrupt code might not like the system call vector. */
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if (!check_syscall_vector(lg))
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kill_guest(lg, "bad syscall vector");
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return 0;
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}
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/* Now we've examined the hypercall code; our Guest can make requests. There
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@ -48,6 +48,9 @@ struct lguest_data
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/* Fields initialized by the Guest at boot: */
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/* Instruction range to suppress interrupts even if enabled */
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unsigned long noirq_start, noirq_end;
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/* The vector to try to use for system calls (0x40 or 0x80). */
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unsigned int syscall_vec;
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};
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extern struct lguest_data lguest_data;
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#endif /* __ASSEMBLY__ */
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