bitkeeper revision 1.397 (3f4e025cTStPJGtnPMTvJ95GFn4NAg)

mm.h, config.h, hypervisor-if.h, desc.h, trampoline.S, mm.c, boot.S:
  Move reserved GDT entries to later in the GDT, allowing support for hard-coded small selector values in brain-dead OSes.

7 files changed, 56 insertions, 34 deletions

diff --git a/xen/arch/i386/boot/boot.S b/xen/arch/i386/boot/boot.S
index 64658d6aa8..b27ff6c0f2 100644
--- a/xen/arch/i386/boot/boot.S
+++ b/xen/arch/i386/boot/boot.S
@@ -1,4 +1,5 @@
 #include <xeno/config.h>
+#include <hypervisor-ifs/hypervisor-if.h>
 #include <asm/page.h>
 
 #define  SECONDARY_CPU_FLAG 0xA5A5A5A5
@@ -229,26 +230,27 @@ SYMBOL_NAME(idt):
 
         .word   0
 gdt_descr:
-	.word	(2*NR_CPUS+8)*8-1
+	.word	(LAST_RESERVED_GDT_ENTRY*8)+7
 SYMBOL_NAME(gdt):       
         .long   SYMBOL_NAME(gdt_table)	/* gdt base */
 
         .word   0
 nopaging_gdt_descr:
-        .word   (2*NR_CPUS+8)*8-1
+        .word   (LAST_RESERVED_GDT_ENTRY*8)+7
         .long   SYMBOL_NAME(gdt_table)-__PAGE_OFFSET
         
         ALIGN
 /* NB. Rings != 0 get access up to 0xFC400000. This allows access to the */
 /*     machine->physical mapping table. Ring 0 can access all memory.    */
 ENTRY(gdt_table)
-        .quad 0x0000000000000000     /* 0x0000 NULL descriptor */
-        .quad 0x00cf9a000000ffff     /* 0x0008 ring 0 4.00GB code at 0x0 */
-        .quad 0x00cf92000000ffff     /* 0x0010 ring 0 4.00GB data at 0x0 */
-        .quad 0x00cfba000000c3ff     /* 0x0019 ring 1 3.95GB code at 0x0 */
-        .quad 0x00cfb2000000c3ff     /* 0x0021 ring 1 3.95GB data at 0x0 */
-        .quad 0x00cffa000000c3ff     /* 0x002b ring 3 3.95GB code at 0x0 */
-        .quad 0x00cff2000000c3ff     /* 0x0033 ring 3 3.95GB data at 0x0 */
+        .fill FIRST_RESERVED_GDT_ENTRY,8,0
+        .quad 0x0000000000000000     /* unused */
+        .quad 0x00cf9a000000ffff     /* 0x0808 ring 0 4.00GB code at 0x0 */
+        .quad 0x00cf92000000ffff     /* 0x0810 ring 0 4.00GB data at 0x0 */
+        .quad 0x00cfba000000c3ff     /* 0x0819 ring 1 3.95GB code at 0x0 */
+        .quad 0x00cfb2000000c3ff     /* 0x0821 ring 1 3.95GB data at 0x0 */
+        .quad 0x00cffa000000c3ff     /* 0x082b ring 3 3.95GB code at 0x0 */
+        .quad 0x00cff2000000c3ff     /* 0x0833 ring 3 3.95GB data at 0x0 */
         .quad 0x0000000000000000     /* unused                           */
         .fill 2*NR_CPUS,8,0          /* space for TSS and LDT per CPU    */
 
diff --git a/xen/arch/i386/mm.c b/xen/arch/i386/mm.c
index b32650c614..2ccb1bda1f 100644
--- a/xen/arch/i386/mm.c
+++ b/xen/arch/i386/mm.c
@@ -188,7 +188,7 @@ long do_set_gdt(unsigned long *frame_list, unsigned int entries)
     long ret = -EINVAL;
     struct pfn_info *page;
 
-    if ( (entries < FIRST_DOMAIN_GDT_ENTRY) || (entries > 8192) ) 
+    if ( (entries <= LAST_RESERVED_GDT_ENTRY) || (entries > 8192) ) 
         return -EINVAL;
 
     if ( copy_from_user(frames, frame_list, nr_pages * sizeof(unsigned long)) )
@@ -249,8 +249,10 @@ long do_set_gdt(unsigned long *frame_list, unsigned int entries)
 
     local_flush_tlb();
 
-    /* Copy over first entries of the new GDT. */
-    memcpy((void *)GDT_VIRT_START, gdt_table, FIRST_DOMAIN_GDT_ENTRY*8);
+    /* Copy reserved GDT entries to the new GDT. */
+    memcpy((struct desc_struct *)GDT_VIRT_START + FIRST_RESERVED_GDT_ENTRY, 
+           gdt_table + FIRST_RESERVED_GDT_ENTRY, 
+           NR_RESERVED_GDT_ENTRIES*8);
     
     SET_GDT_ADDRESS(current, GDT_VIRT_START);
     SET_GDT_ENTRIES(current, (entries*8)-1);
@@ -284,9 +286,10 @@ long do_update_descriptor(
     switch ( (page->flags & PG_type_mask) )
     {
     case PGT_gdt_page:
-        /* Disallow updates of Xen-private descriptors in the current GDT. */
+        /* Disallow updates of Xen-reserved descriptors in the current GDT. */
         if ( (l1_pgentry_to_pagenr(current->mm.perdomain_pt[0]) == pfn) &&
-             (((pa&(PAGE_SIZE-1))>>3) < FIRST_DOMAIN_GDT_ENTRY) )
+             (((pa&(PAGE_SIZE-1))>>3) >= FIRST_RESERVED_GDT_ENTRY) &&
+             (((pa&(PAGE_SIZE-1))>>3) <= LAST_RESERVED_GDT_ENTRY) )
             goto out;
     case PGT_ldt_page:
     case PGT_writeable_page:
diff --git a/xen/arch/i386/trampoline.S b/xen/arch/i386/trampoline.S
index 79f58d746c..9fdea7d679 100644
--- a/xen/arch/i386/trampoline.S
+++ b/xen/arch/i386/trampoline.S
@@ -16,6 +16,7 @@
  */
 
 #include <xeno/config.h>
+#include <hypervisor-ifs/hypervisor-if.h>
 #include <asm/page.h>
 
 #ifdef CONFIG_SMP
@@ -49,8 +50,8 @@ idt_48:
 	.word	0, 0			# idt base = 0L
 
 gdt_48:
-	.word	0x0800			# gdt limit = 2048, 256 GDT entries
-	.long	gdt_table-__PAGE_OFFSET	# gdt base = gdt (first SMP CPU)
+	.word	(LAST_RESERVED_GDT_ENTRY*8)+7
+	.long	gdt_table-__PAGE_OFFSET
 
 .globl SYMBOL_NAME(trampoline_end)
 SYMBOL_NAME_LABEL(trampoline_end)
diff --git a/xen/include/asm-i386/desc.h b/xen/include/asm-i386/desc.h
index 3155af3268..facb3a6452 100644
--- a/xen/include/asm-i386/desc.h
+++ b/xen/include/asm-i386/desc.h
@@ -3,8 +3,8 @@
 
 #define LDT_ENTRY_SIZE 8
 
-#define __FIRST_TSS_ENTRY 8
-#define __FIRST_LDT_ENTRY (__FIRST_TSS_ENTRY+1)
+#define __FIRST_TSS_ENTRY (FIRST_RESERVED_GDT_ENTRY + 8)
+#define __FIRST_LDT_ENTRY (__FIRST_TSS_ENTRY + 1)
 
 #define __TSS(n) (((n)<<1) + __FIRST_TSS_ENTRY)
 #define __LDT(n) (((n)<<1) + __FIRST_LDT_ENTRY)
@@ -14,15 +14,19 @@
 /*
  * Guest OS must provide its own code selectors, or use the one we provide.
  * The RPL must be 1, as we only create bounce frames to ring 1.
+ * Any LDT selector value is okay.
  */
-#define VALID_CODESEL(_s)                                                  \
-    (((((_s)>>2) >= FIRST_DOMAIN_GDT_ENTRY) || ((_s) == FLAT_RING1_CS)) && \
-     (((_s)&3) == 1))
 
-#define VALID_DATASEL(_s)                                                  \
-    (((((_s)>>2) >= FIRST_DOMAIN_GDT_ENTRY) || ((_s) == FLAT_RING1_DS)) && \
+#define VALID_SEL(_s)                                                      \
+    (((((_s)>>3) < FIRST_RESERVED_GDT_ENTRY) ||                            \
+      (((_s)>>3) >  LAST_RESERVED_GDT_ENTRY) ||                            \
+      ((_s)&4)) &&                                                         \
      (((_s)&3) == 1))
 
+#define VALID_CODESEL(_s) ((_s) == FLAT_RING1_CS || VALID_SEL(_s))
+
+#define VALID_DATASEL(_s) ((_s) == FLAT_RING1_DS || VALID_SEL(_s))
+
 /* These are bitmasks for the first 32 bits of a descriptor table entry. */
 #define _SEGMENT_TYPE    (15<< 8)
 #define _SEGMENT_S       ( 1<<12) /* System descriptor (yes iff S==0) */
diff --git a/xen/include/hypervisor-ifs/hypervisor-if.h b/xen/include/hypervisor-ifs/hypervisor-if.h
index 64c5bc040a..97eebaa014 100644
--- a/xen/include/hypervisor-ifs/hypervisor-if.h
+++ b/xen/include/hypervisor-ifs/hypervisor-if.h
@@ -10,17 +10,29 @@
 /*
  * SEGMENT DESCRIPTOR TABLES
  */
-/* The first few GDT entries are reserved by Xen. */
-#define FIRST_DOMAIN_GDT_ENTRY	40
 /*
- * These flat segments are in the Xen-private section of every GDT. Since 
- * these are also present in the initial GDT, many OSes will be able to avoid 
+ * A number of GDT entries are reserved by Xen. These are not situated at the
+ * start of the GDT because some stupid OSes export hard-coded selector values
+ * in their ABI. These hard-coded values are always near the start of the GDT,
+ * so Xen places itself out of the way.
+ * 
+ * NB. The reserved range is inclusive (that is, both FIRST_RESERVED_GDT_ENTRY
+ * and LAST_RESERVED_GDT_ENTRY are reserved).
+ */
+#define NR_RESERVED_GDT_ENTRIES         40
+#define FIRST_RESERVED_GDT_ENTRY	256
+#define LAST_RESERVED_GDT_ENTRY         \
+  (FIRST_RESERVED_GDT_ENTRY + NR_RESERVED_GDT_ENTRIES - 1)
+
+/*
+ * These flat segments are in the Xen-private section of every GDT. Since these
+ * are also present in the initial GDT, many OSes will be able to avoid
  * installing their own GDT.
  */
-#define FLAT_RING1_CS		0x0019
-#define FLAT_RING1_DS		0x0021
-#define FLAT_RING3_CS		0x002b
-#define FLAT_RING3_DS		0x0033
+#define FLAT_RING1_CS		0x0819
+#define FLAT_RING1_DS		0x0821
+#define FLAT_RING3_CS		0x082b
+#define FLAT_RING3_DS		0x0833
 
 
 /*
diff --git a/xen/include/xeno/config.h b/xen/include/xeno/config.h
index f1bc4c2000..b4935f706f 100644
--- a/xen/include/xeno/config.h
+++ b/xen/include/xeno/config.h
@@ -127,8 +127,8 @@
 
 #define barrier() __asm__ __volatile__("": : :"memory")
 
-#define __HYPERVISOR_CS 0x0008
-#define __HYPERVISOR_DS 0x0010
+#define __HYPERVISOR_CS 0x0808
+#define __HYPERVISOR_DS 0x0810
 
 #define NR_syscalls 256
 
diff --git a/xen/include/xeno/mm.h b/xen/include/xeno/mm.h
index 6f7eaa89b7..2570cfafec 100644
--- a/xen/include/xeno/mm.h
+++ b/xen/include/xeno/mm.h
@@ -149,7 +149,7 @@ int check_descriptor(unsigned long a, unsigned long b);
 /* Part of the domain API. */
 int do_process_page_updates(page_update_request_t *updates, int count);
 
-#define DEFAULT_GDT_ENTRIES     ((FIRST_DOMAIN_GDT_ENTRY*8)-1)
+#define DEFAULT_GDT_ENTRIES     ((LAST_RESERVED_GDT_ENTRY*8)+7)
 #define DEFAULT_GDT_ADDRESS     ((unsigned long)gdt_table)
 
 #endif /* __XENO_MM_H__ */