Commit 72d64cc7 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

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: default avatarAndy 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: default avatarIngo Molnar <mingo@kernel.org>
parent dca5b52a

arch/x86/include/asm/segment.h

+141 −101
Original line number Diff line number Diff line
@@ -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) |	\
@@ -12,7 +14,7 @@ 
	 (((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
@@ -21,56 +23,63 @@ 
#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 */

#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
@@ -97,31 +106,48 @@ 


#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 __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 */



/* 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)

#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

#endif



#define GDT_ENTRIES 32



#else /* 64-bit: */



#include <asm/cache.h>
@@ -129,45 +155,63 @@ 
#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:

 * 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_TSS		8  /* needs two entries */

#define GDT_ENTRY_LDT		10 /* needs two entries */

/* Needs two entries */

#define GDT_ENTRY_TSS			8

/* Needs two entries */

#define GDT_ENTRY_LDT			10



#define GDT_ENTRY_TLS_MIN		12

#define GDT_ENTRY_TLS_MAX		14



#define GDT_ENTRY_PER_CPU	15 /* abused to load per CPU data from limit */

/* Abused to load per CPU data from limit */

#define GDT_ENTRY_PER_CPU		15



/* Selectors need to also have a correct RPL (+3 thingy) */

/*

 * Number of entries in the GDT table:

 */

#define GDT_ENTRIES			16



/*

 * 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 __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 __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)



/* TLS indexes for 64bit - hardcoded in arch_prctl */

/* 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)



#define GDT_ENTRIES 16



#endif



#ifndef CONFIG_PARAVIRT
@@ -176,14 +220,17 @@ 


#define IDT_ENTRIES			256

#define NUM_EXCEPTION_VECTORS		32

/* Bitmask of exception vectors which push an error code on the stack */



/* 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
@@ -211,13 +258,13 @@ do { \ 
} 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
@@ -235,13 +282,6 @@ do { \ 
# 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__ */

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