From f2f30ebca6c0c95e987cb9a1fd1495770a75432e Mon Sep 17 00:00:00 2001 From: Zachary Amsden Date: Sat, 3 Sep 2005 15:56:47 -0700 Subject: [PATCH] [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 --- arch/i386/kernel/ldt.c | 7 ++----- include/asm-i386/desc.h | 7 +++++++ 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 -- 2.20.1