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>
This commit is contained in:
Rusty Russell 2007-10-22 11:03:35 +10:00
parent ee3db0f2b6
commit c18acd73ff
6 changed files with 79 additions and 11 deletions

View file

@ -87,6 +87,7 @@ struct lguest_data lguest_data = {
.noirq_start = (u32)lguest_noirq_start,
.noirq_end = (u32)lguest_noirq_end,
.blocked_interrupts = { 1 }, /* Block timer interrupts */
.syscall_vec = SYSCALL_VECTOR,
};
static cycle_t clock_base;

View file

@ -281,37 +281,47 @@ static int __init init(void)
/* First we put the Switcher up in very high virtual memory. */
err = map_switcher();
if (err)
return err;
goto out;
/* Now we set up the pagetable implementation for the Guests. */
err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
if (err) {
unmap_switcher();
return err;
}
if (err)
goto unmap;
/* The I/O subsystem needs some things initialized. */
lguest_io_init();
/* We might need to reserve an interrupt vector. */
err = init_interrupts();
if (err)
goto free_pgtables;
/* /dev/lguest needs to be registered. */
err = lguest_device_init();
if (err) {
free_pagetables();
unmap_switcher();
return err;
}
if (err)
goto free_interrupts;
/* Finally we do some architecture-specific setup. */
lguest_arch_host_init();
/* All good! */
return 0;
free_interrupts:
free_interrupts();
free_pgtables:
free_pagetables();
unmap:
unmap_switcher();
out:
return err;
}
/* Cleaning up is just the same code, backwards. With a little French. */
static void __exit fini(void)
{
lguest_device_remove();
free_interrupts();
free_pagetables();
unmap_switcher();

View file

@ -12,8 +12,14 @@
* them first, so we also have a way of "reflecting" them into the Guest as if
* they had been delivered to it directly. :*/
#include <linux/uaccess.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include "lg.h"
/* Allow Guests to use a non-128 (ie. non-Linux) syscall trap. */
static unsigned int syscall_vector = SYSCALL_VECTOR;
module_param(syscall_vector, uint, 0444);
/* The address of the interrupt handler is split into two bits: */
static unsigned long idt_address(u32 lo, u32 hi)
{
@ -183,6 +189,47 @@ void maybe_do_interrupt(struct lguest *lg)
* timer interrupt. */
write_timestamp(lg);
}
/*:*/
/* Linux uses trap 128 for system calls. Plan9 uses 64, and Ron Minnich sent
* me a patch, so we support that too. It'd be a big step for lguest if half
* the Plan 9 user base were to start using it.
*
* Actually now I think of it, it's possible that Ron *is* half the Plan 9
* userbase. Oh well. */
static bool could_be_syscall(unsigned int num)
{
/* Normal Linux SYSCALL_VECTOR or reserved vector? */
return num == SYSCALL_VECTOR || num == syscall_vector;
}
/* The syscall vector it wants must be unused by Host. */
bool check_syscall_vector(struct lguest *lg)
{
u32 vector;
if (get_user(vector, &lg->lguest_data->syscall_vec))
return false;
return could_be_syscall(vector);
}
int init_interrupts(void)
{
/* If they want some strange system call vector, reserve it now */
if (syscall_vector != SYSCALL_VECTOR
&& test_and_set_bit(syscall_vector, used_vectors)) {
printk("lg: couldn't reserve syscall %u\n", syscall_vector);
return -EBUSY;
}
return 0;
}
void free_interrupts(void)
{
if (syscall_vector != SYSCALL_VECTOR)
clear_bit(syscall_vector, used_vectors);
}
/*H:220 Now we've got the routines to deliver interrupts, delivering traps
* like page fault is easy. The only trick is that Intel decided that some
@ -224,7 +271,7 @@ static int direct_trap(unsigned int num)
{
/* Hardware interrupts don't go to the Guest at all (except system
* call). */
if (num >= FIRST_EXTERNAL_VECTOR && num != SYSCALL_VECTOR)
if (num >= FIRST_EXTERNAL_VECTOR && !could_be_syscall(num))
return 0;
/* The Host needs to see page faults (for shadow paging and to save the

View file

@ -141,6 +141,9 @@ void copy_traps(const struct lguest *lg, struct desc_struct *idt,
const unsigned long *def);
void guest_set_clockevent(struct lguest *lg, unsigned long delta);
void init_clockdev(struct lguest *lg);
bool check_syscall_vector(struct lguest *lg);
int init_interrupts(void);
void free_interrupts(void);
/* segments.c: */
void setup_default_gdt_entries(struct lguest_ro_state *state);

View file

@ -530,6 +530,10 @@ int lguest_arch_init_hypercalls(struct lguest *lg)
if (put_user(tsc_speed, &lg->lguest_data->tsc_khz))
return -EFAULT;
/* The interrupt code might not like the system call vector. */
if (!check_syscall_vector(lg))
kill_guest(lg, "bad syscall vector");
return 0;
}
/* Now we've examined the hypercall code; our Guest can make requests. There

View file

@ -48,6 +48,9 @@ struct lguest_data
/* Fields initialized by the Guest at boot: */
/* Instruction range to suppress interrupts even if enabled */
unsigned long noirq_start, noirq_end;
/* The vector to try to use for system calls (0x40 or 0x80). */
unsigned int syscall_vec;
};
extern struct lguest_data lguest_data;
#endif /* __ASSEMBLY__ */