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Allow guest to specify syscall vector to use.

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(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
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49
drivers/lguest/interrupts_and_traps.c
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