From f2f30ebca6c0c95e987cb9a1fd1495770a75432e Mon Sep 17 00:00:00 2001 From: Zachary Amsden Date: Sat, 3 Sep 2005 15:56:47 -0700 Subject: [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 #include #include #include #include #include #include #define __KERNEL__ #include 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/asm-i386/desc.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'include') diff --git a/include/asm-i386/desc.h b/include/asm-i386/desc.h index ccb11c03283..6df1a53c190 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 -- cgit v1.2.3