x86/asm: Further improve segment.h readability
- extend/clarify explanations where necessary
- move comments from macro values to before the macro, to
make them more consistent, and to reduce preprocessor overhead
- sort GDT index and selector values likewise by number
- use consistent, modern kernel coding style across the file
- capitalize consistently
- use consistent vertical spacing
- remove the unused get_limit() method (noticed by Andy Lutomirski)
No change in code (verified with objdump -d):
64-bit defconfig+kvmconfig:
815a129bc1f80de6445c1d8ca5b97cad vmlinux.o.before.asm
815a129bc1f80de6445c1d8ca5b97cad vmlinux.o.after.asm
32-bit defconfig+kvmconfig:
e659ef045159ddf41a0771b33a34aae5 vmlinux.o.before.asm
e659ef045159ddf41a0771b33a34aae5 vmlinux.o.after.asm
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h
index 117028f..d394899 100644
--- a/arch/x86/include/asm/segment.h
+++ b/arch/x86/include/asm/segment.h
@@ -3,8 +3,10 @@
#include <linux/const.h>
-/* Constructor for a conventional segment GDT (or LDT) entry */
-/* This is a macro so it can be used in initializers */
+/*
+ * Constructor for a conventional segment GDT (or LDT) entry.
+ * This is a macro so it can be used in initializers.
+ */
#define GDT_ENTRY(flags, base, limit) \
((((base) & _AC(0xff000000,ULL)) << (56-24)) | \
(((flags) & _AC(0x0000f0ff,ULL)) << 40) | \
@@ -12,71 +14,78 @@
(((base) & _AC(0x00ffffff,ULL)) << 16) | \
(((limit) & _AC(0x0000ffff,ULL))))
-/* Simple and small GDT entries for booting only */
+/* Simple and small GDT entries for booting only: */
#define GDT_ENTRY_BOOT_CS 2
#define GDT_ENTRY_BOOT_DS 3
#define GDT_ENTRY_BOOT_TSS 4
-#define __BOOT_CS (GDT_ENTRY_BOOT_CS * 8)
-#define __BOOT_DS (GDT_ENTRY_BOOT_DS * 8)
-#define __BOOT_TSS (GDT_ENTRY_BOOT_TSS * 8)
+#define __BOOT_CS (GDT_ENTRY_BOOT_CS*8)
+#define __BOOT_DS (GDT_ENTRY_BOOT_DS*8)
+#define __BOOT_TSS (GDT_ENTRY_BOOT_TSS*8)
-#define SEGMENT_RPL_MASK 0x3 /*
- * Bottom two bits of selector give the ring
- * privilege level
- */
-#define SEGMENT_TI_MASK 0x4 /* Bit 2 is table indicator (LDT/GDT) */
-#define USER_RPL 0x3 /* User mode is privilege level 3 */
-#define SEGMENT_LDT 0x4 /* LDT segment has TI set... */
-#define SEGMENT_GDT 0x0 /* ... GDT has it cleared */
+/*
+ * Bottom two bits of selector give the ring
+ * privilege level
+ */
+#define SEGMENT_RPL_MASK 0x3
+
+/* User mode is privilege level 3: */
+#define USER_RPL 0x3
+
+/* Bit 2 is Table Indicator (TI): selects between LDT or GDT */
+#define SEGMENT_TI_MASK 0x4
+/* LDT segment has TI set ... */
+#define SEGMENT_LDT 0x4
+/* ... GDT has it cleared */
+#define SEGMENT_GDT 0x0
#ifdef CONFIG_X86_32
/*
* The layout of the per-CPU GDT under Linux:
*
- * 0 - null
+ * 0 - null <=== cacheline #1
* 1 - reserved
* 2 - reserved
* 3 - reserved
*
- * 4 - unused <==== new cacheline
+ * 4 - unused <=== cacheline #2
* 5 - unused
*
* ------- start of TLS (Thread-Local Storage) segments:
*
* 6 - TLS segment #1 [ glibc's TLS segment ]
* 7 - TLS segment #2 [ Wine's %fs Win32 segment ]
- * 8 - TLS segment #3
+ * 8 - TLS segment #3 <=== cacheline #3
* 9 - reserved
* 10 - reserved
* 11 - reserved
*
* ------- start of kernel segments:
*
- * 12 - kernel code segment <==== new cacheline
+ * 12 - kernel code segment <=== cacheline #4
* 13 - kernel data segment
* 14 - default user CS
* 15 - default user DS
- * 16 - TSS
+ * 16 - TSS <=== cacheline #5
* 17 - LDT
* 18 - PNPBIOS support (16->32 gate)
* 19 - PNPBIOS support
- * 20 - PNPBIOS support
+ * 20 - PNPBIOS support <=== cacheline #6
* 21 - PNPBIOS support
* 22 - PNPBIOS support
* 23 - APM BIOS support
- * 24 - APM BIOS support
+ * 24 - APM BIOS support <=== cacheline #7
* 25 - APM BIOS support
*
* 26 - ESPFIX small SS
* 27 - per-cpu [ offset to per-cpu data area ]
- * 28 - stack_canary-20 [ for stack protector ]
+ * 28 - stack_canary-20 [ for stack protector ] <=== cacheline #8
* 29 - unused
* 30 - unused
* 31 - TSS for double fault handler
*/
-#define GDT_ENTRY_TLS_MIN 6
-#define GDT_ENTRY_TLS_MAX (GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)
+#define GDT_ENTRY_TLS_MIN 6
+#define GDT_ENTRY_TLS_MAX (GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)
#define GDT_ENTRY_KERNEL_CS 12
#define GDT_ENTRY_KERNEL_DS 13
@@ -97,96 +106,134 @@
#define GDT_ENTRY_DOUBLEFAULT_TSS 31
+/*
+ * Number of entries in the GDT table:
+ */
+#define GDT_ENTRIES 32
+
+/*
+ * Segment selector values corresponding to the above entries:
+ */
+
#define __KERNEL_CS (GDT_ENTRY_KERNEL_CS*8)
#define __KERNEL_DS (GDT_ENTRY_KERNEL_DS*8)
-#define __USER_DS (GDT_ENTRY_DEFAULT_USER_DS*8+3)
-#define __USER_CS (GDT_ENTRY_DEFAULT_USER_CS*8+3)
+#define __USER_DS (GDT_ENTRY_DEFAULT_USER_DS*8 + 3)
+#define __USER_CS (GDT_ENTRY_DEFAULT_USER_CS*8 + 3)
#define __ESPFIX_SS (GDT_ENTRY_ESPFIX_SS*8)
-#define PNP_CS32 (GDT_ENTRY_PNPBIOS_CS32 * 8) /* segment for calling fn */
-#define PNP_CS16 (GDT_ENTRY_PNPBIOS_CS16 * 8) /* code segment for BIOS */
+
+/* segment for calling fn: */
+#define PNP_CS32 (GDT_ENTRY_PNPBIOS_CS32*8)
+/* code segment for BIOS: */
+#define PNP_CS16 (GDT_ENTRY_PNPBIOS_CS16*8)
+
/* "Is this PNP code selector (PNP_CS32 or PNP_CS16)?" */
-#define SEGMENT_IS_PNP_CODE(x) (((x) & 0xf4) == PNP_CS32)
-#define PNP_DS (GDT_ENTRY_PNPBIOS_DS * 8) /* data segment for BIOS */
-#define PNP_TS1 (GDT_ENTRY_PNPBIOS_TS1 * 8) /* transfer data segment */
-#define PNP_TS2 (GDT_ENTRY_PNPBIOS_TS2 * 8) /* another data segment */
+#define SEGMENT_IS_PNP_CODE(x) (((x) & 0xf4) == PNP_CS32)
+
+/* data segment for BIOS: */
+#define PNP_DS (GDT_ENTRY_PNPBIOS_DS*8)
+/* transfer data segment: */
+#define PNP_TS1 (GDT_ENTRY_PNPBIOS_TS1*8)
+/* another data segment: */
+#define PNP_TS2 (GDT_ENTRY_PNPBIOS_TS2*8)
+
#ifdef CONFIG_SMP
-#define __KERNEL_PERCPU (GDT_ENTRY_PERCPU*8)
+# define __KERNEL_PERCPU (GDT_ENTRY_PERCPU*8)
#else
-#define __KERNEL_PERCPU 0
-#endif
-#ifdef CONFIG_CC_STACKPROTECTOR
-#define __KERNEL_STACK_CANARY (GDT_ENTRY_STACK_CANARY*8)
-#else
-#define __KERNEL_STACK_CANARY 0
+# define __KERNEL_PERCPU 0
#endif
-#define GDT_ENTRIES 32
+#ifdef CONFIG_CC_STACKPROTECTOR
+# define __KERNEL_STACK_CANARY (GDT_ENTRY_STACK_CANARY*8)
+#else
+# define __KERNEL_STACK_CANARY 0
+#endif
#else /* 64-bit: */
#include <asm/cache.h>
-#define GDT_ENTRY_KERNEL32_CS 1
-#define GDT_ENTRY_KERNEL_CS 2
-#define GDT_ENTRY_KERNEL_DS 3
+#define GDT_ENTRY_KERNEL32_CS 1
+#define GDT_ENTRY_KERNEL_CS 2
+#define GDT_ENTRY_KERNEL_DS 3
+
/*
- * we cannot use the same code segment descriptor for user and kernel
- * -- not even in the long flat mode, because of different DPL /kkeil
- * GDT layout to get 64bit syscall/sysret right. sysret hardcodes selectors:
- * if returning to 32-bit userspace: cs = STAR.SYSRET_CS,
- * if returning to 64-bit userspace: cs = STAR.SYSRET_CS+16,
+ * We cannot use the same code segment descriptor for user and kernel mode,
+ * not even in long flat mode, because of different DPL.
+ *
+ * GDT layout to get 64-bit SYSCALL/SYSRET support right. SYSRET hardcodes
+ * selectors:
+ *
+ * if returning to 32-bit userspace: cs = STAR.SYSRET_CS,
+ * if returning to 64-bit userspace: cs = STAR.SYSRET_CS+16,
+ *
* ss = STAR.SYSRET_CS+8 (in either case)
+ *
* thus USER_DS should be between 32-bit and 64-bit code selectors:
*/
-#define GDT_ENTRY_DEFAULT_USER32_CS 4
-#define GDT_ENTRY_DEFAULT_USER_DS 5
-#define GDT_ENTRY_DEFAULT_USER_CS 6
+#define GDT_ENTRY_DEFAULT_USER32_CS 4
+#define GDT_ENTRY_DEFAULT_USER_DS 5
+#define GDT_ENTRY_DEFAULT_USER_CS 6
-#define GDT_ENTRY_TSS 8 /* needs two entries */
-#define GDT_ENTRY_LDT 10 /* needs two entries */
-#define GDT_ENTRY_TLS_MIN 12
-#define GDT_ENTRY_TLS_MAX 14
+/* Needs two entries */
+#define GDT_ENTRY_TSS 8
+/* Needs two entries */
+#define GDT_ENTRY_LDT 10
-#define GDT_ENTRY_PER_CPU 15 /* abused to load per CPU data from limit */
+#define GDT_ENTRY_TLS_MIN 12
+#define GDT_ENTRY_TLS_MAX 14
-/* Selectors need to also have a correct RPL (+3 thingy) */
-#define __KERNEL_CS (GDT_ENTRY_KERNEL_CS*8)
-#define __KERNEL_DS (GDT_ENTRY_KERNEL_DS*8)
-#define __USER_DS (GDT_ENTRY_DEFAULT_USER_DS*8+3)
-#define __USER_CS (GDT_ENTRY_DEFAULT_USER_CS*8+3)
-#define __KERNEL32_CS (GDT_ENTRY_KERNEL32_CS*8)
-#define __USER32_CS (GDT_ENTRY_DEFAULT_USER32_CS*8+3)
-#define __USER32_DS __USER_DS
-#define __PER_CPU_SEG (GDT_ENTRY_PER_CPU*8+3)
+/* Abused to load per CPU data from limit */
+#define GDT_ENTRY_PER_CPU 15
-/* TLS indexes for 64bit - hardcoded in arch_prctl */
-#define FS_TLS 0
-#define GS_TLS 1
+/*
+ * Number of entries in the GDT table:
+ */
+#define GDT_ENTRIES 16
-#define GS_TLS_SEL ((GDT_ENTRY_TLS_MIN+GS_TLS)*8 + 3)
-#define FS_TLS_SEL ((GDT_ENTRY_TLS_MIN+FS_TLS)*8 + 3)
+/*
+ * Segment selector values corresponding to the above entries:
+ *
+ * Note, selectors also need to have a correct RPL,
+ * expressed with the +3 value for user-space selectors:
+ */
+#define __KERNEL32_CS (GDT_ENTRY_KERNEL32_CS*8)
+#define __KERNEL_CS (GDT_ENTRY_KERNEL_CS*8)
+#define __KERNEL_DS (GDT_ENTRY_KERNEL_DS*8)
+#define __USER32_CS (GDT_ENTRY_DEFAULT_USER32_CS*8 + 3)
+#define __USER_DS (GDT_ENTRY_DEFAULT_USER_DS*8 + 3)
+#define __USER32_DS __USER_DS
+#define __USER_CS (GDT_ENTRY_DEFAULT_USER_CS*8 + 3)
+#define __PER_CPU_SEG (GDT_ENTRY_PER_CPU*8 + 3)
-#define GDT_ENTRIES 16
+/* TLS indexes for 64-bit - hardcoded in arch_prctl(): */
+#define FS_TLS 0
+#define GS_TLS 1
+
+#define GS_TLS_SEL ((GDT_ENTRY_TLS_MIN+GS_TLS)*8 + 3)
+#define FS_TLS_SEL ((GDT_ENTRY_TLS_MIN+FS_TLS)*8 + 3)
#endif
#ifndef CONFIG_PARAVIRT
-#define get_kernel_rpl() 0
+# define get_kernel_rpl() 0
#endif
-#define IDT_ENTRIES 256
-#define NUM_EXCEPTION_VECTORS 32
-/* Bitmask of exception vectors which push an error code on the stack */
-#define EXCEPTION_ERRCODE_MASK 0x00027d00
-#define GDT_SIZE (GDT_ENTRIES * 8)
-#define GDT_ENTRY_TLS_ENTRIES 3
-#define TLS_SIZE (GDT_ENTRY_TLS_ENTRIES * 8)
+#define IDT_ENTRIES 256
+#define NUM_EXCEPTION_VECTORS 32
+
+/* Bitmask of exception vectors which push an error code on the stack: */
+#define EXCEPTION_ERRCODE_MASK 0x00027d00
+
+#define GDT_SIZE (GDT_ENTRIES*8)
+#define GDT_ENTRY_TLS_ENTRIES 3
+#define TLS_SIZE (GDT_ENTRY_TLS_ENTRIES* 8)
#ifdef __KERNEL__
#ifndef __ASSEMBLY__
+
extern const char early_idt_handlers[NUM_EXCEPTION_VECTORS][2+2+5];
#ifdef CONFIG_TRACING
-#define trace_early_idt_handlers early_idt_handlers
+# define trace_early_idt_handlers early_idt_handlers
#endif
/*
@@ -211,37 +258,30 @@
} while (0)
/*
- * Save a segment register away
+ * Save a segment register away:
*/
#define savesegment(seg, value) \
asm("mov %%" #seg ",%0":"=r" (value) : : "memory")
/*
- * x86_32 user gs accessors.
+ * x86-32 user GS accessors:
*/
#ifdef CONFIG_X86_32
-#ifdef CONFIG_X86_32_LAZY_GS
-#define get_user_gs(regs) (u16)({unsigned long v; savesegment(gs, v); v;})
-#define set_user_gs(regs, v) loadsegment(gs, (unsigned long)(v))
-#define task_user_gs(tsk) ((tsk)->thread.gs)
-#define lazy_save_gs(v) savesegment(gs, (v))
-#define lazy_load_gs(v) loadsegment(gs, (v))
-#else /* X86_32_LAZY_GS */
-#define get_user_gs(regs) (u16)((regs)->gs)
-#define set_user_gs(regs, v) do { (regs)->gs = (v); } while (0)
-#define task_user_gs(tsk) (task_pt_regs(tsk)->gs)
-#define lazy_save_gs(v) do { } while (0)
-#define lazy_load_gs(v) do { } while (0)
-#endif /* X86_32_LAZY_GS */
+# ifdef CONFIG_X86_32_LAZY_GS
+# define get_user_gs(regs) (u16)({ unsigned long v; savesegment(gs, v); v; })
+# define set_user_gs(regs, v) loadsegment(gs, (unsigned long)(v))
+# define task_user_gs(tsk) ((tsk)->thread.gs)
+# define lazy_save_gs(v) savesegment(gs, (v))
+# define lazy_load_gs(v) loadsegment(gs, (v))
+# else /* X86_32_LAZY_GS */
+# define get_user_gs(regs) (u16)((regs)->gs)
+# define set_user_gs(regs, v) do { (regs)->gs = (v); } while (0)
+# define task_user_gs(tsk) (task_pt_regs(tsk)->gs)
+# define lazy_save_gs(v) do { } while (0)
+# define lazy_load_gs(v) do { } while (0)
+# endif /* X86_32_LAZY_GS */
#endif /* X86_32 */
-static inline unsigned long get_limit(unsigned long segment)
-{
- unsigned long __limit;
- asm("lsll %1,%0" : "=r" (__limit) : "r" (segment));
- return __limit + 1;
-}
-
#endif /* !__ASSEMBLY__ */
#endif /* __KERNEL__ */