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authorZachary Amsden <zach@vmware.com>2005-09-03 15:56:47 -0700
committerLinus Torvalds <torvalds@evo.osdl.org>2005-09-05 00:06:13 -0700
commitf2f30ebca6c0c95e987cb9a1fd1495770a75432e (patch)
treeea7b1763aa0e0d36b52fa245449c79338fe735b3
parente9f86e351fda5b3c40192fc3990453613f160779 (diff)
[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>
-rw-r--r--arch/i386/kernel/ldt.c7
-rw-r--r--include/asm-i386/desc.h7
2 files changed, 9 insertions, 5 deletions
diff --git a/arch/i386/kernel/ldt.c b/arch/i386/kernel/ldt.c
index bb50afbee921..fe1ffa55587d 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:
diff --git a/include/asm-i386/desc.h b/include/asm-i386/desc.h
index ccb11c032839..6df1a53c190e 100644
--- a/include/asm-i386/desc.h
+++ b/include/asm-i386/desc.h
@@ -96,6 +96,13 @@ static inline void set_ldt_desc(unsigned int cpu, void *addr, unsigned int size)
(info)->seg_not_present == 1 && \
(info)->useable == 0 )
+static inline void write_ldt_entry(void *ldt, int entry, __u32 entry_a, __u32 entry_b)
+{
+ __u32 *lp = (__u32 *)((char *)ldt + entry*8);
+ *lp = entry_a;
+ *(lp+1) = entry_b;
+}
+
#if TLS_SIZE != 24
# error update this code.
#endif