diff options
| author | Zachary Amsden <zach@vmware.com> | 2005-09-03 15:56:47 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@evo.osdl.org> | 2005-09-05 00:06:13 -0700 |
| commit | f2f30ebca6c0c95e987cb9a1fd1495770a75432e (patch) | |
| tree | ea7b1763aa0e0d36b52fa245449c79338fe735b3 /arch | |
| parent | e9f86e351fda5b3c40192fc3990453613f160779 (diff) | |
| download | linux-f2f30ebca6c0c95e987cb9a1fd1495770a75432e.tar.gz | |
[PATCH] x86: introduce a write acessor for updating the current LDT
Introduce a write acessor for updating the current LDT. This is required
for hypervisors like Xen that do not allow LDT pages to be directly
written.
Testing - here's a fun little LDT test that can be trivially modified to
test limits as well.
/*
* Copyright (c) 2005, Zachary Amsden (zach@vmware.com)
* This is licensed under the GPL.
*/
#include <stdio.h>
#include <signal.h>
#include <asm/ldt.h>
#include <asm/segment.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/mman.h>
#define __KERNEL__
#include <asm/page.h>
void main(void)
{
struct user_desc desc;
char *code;
unsigned long long tsc;
code = (char *)mmap(0, 8192, PROT_EXEC|PROT_READ|PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
desc.entry_number = 0;
desc.base_addr = code;
desc.limit = 1;
desc.seg_32bit = 1;
desc.contents = MODIFY_LDT_CONTENTS_CODE;
desc.read_exec_only = 0;
desc.limit_in_pages = 1;
desc.seg_not_present = 0;
desc.useable = 1;
if (modify_ldt(1, &desc, sizeof(desc)) != 0) {
perror("modify_ldt");
}
printf("code base is 0x%08x\n", (unsigned)code);
code[0x0ffe] = 0x0f; /* rdtsc */
code[0x0fff] = 0x31;
code[0x1000] = 0xcb; /* lret */
__asm__ __volatile("lcall $7,$0xffe" : "=A" (tsc));
printf("TSC is 0x%016llx\n", tsc);
}
Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/i386/kernel/ldt.c | 7 |
1 files changed, 2 insertions, 5 deletions
diff --git a/arch/i386/kernel/ldt.c b/arch/i386/kernel/ldt.c index bb50afbee921c..fe1ffa55587d4 100644 --- a/arch/i386/kernel/ldt.c +++ b/arch/i386/kernel/ldt.c @@ -177,7 +177,7 @@ static int read_default_ldt(void __user * ptr, unsigned long bytecount) static int write_ldt(void __user * ptr, unsigned long bytecount, int oldmode) { struct mm_struct * mm = current->mm; - __u32 entry_1, entry_2, *lp; + __u32 entry_1, entry_2; int error; struct user_desc ldt_info; @@ -205,8 +205,6 @@ static int write_ldt(void __user * ptr, unsigned long bytecount, int oldmode) goto out_unlock; } - lp = (__u32 *) ((ldt_info.entry_number << 3) + (char *) mm->context.ldt); - /* Allow LDTs to be cleared by the user. */ if (ldt_info.base_addr == 0 && ldt_info.limit == 0) { if (oldmode || LDT_empty(&ldt_info)) { @@ -223,8 +221,7 @@ static int write_ldt(void __user * ptr, unsigned long bytecount, int oldmode) /* Install the new entry ... */ install: - *lp = entry_1; - *(lp+1) = entry_2; + write_ldt_entry(mm->context.ldt, ldt_info.entry_number, entry_1, entry_2); error = 0; out_unlock: |