Commit 88107d33 authored by Mike Rapoport's avatar Mike Rapoport Committed by Linus Torvalds
Browse files

x86/mm: simplify init_trampoline() and surrounding logic 

There are three cases for the trampoline initialization:
* 32-bit does nothing
* 64-bit with kaslr disabled simply copies a PGD entry from the direct map
  to the trampoline PGD
* 64-bit with kaslr enabled maps the real mode trampoline at PUD level

These cases are currently differentiated by a bunch of ifdefs inside
asm/include/pgtable.h and the case of 64-bits with kaslr on uses
pgd_index() helper.

Replacing the ifdefs with a static function in arch/x86/mm/init.c gives
clearer code and allows moving pgd_index() to the generic implementation
in include/linux/pgtable.h

[rppt@linux.ibm.com: take CONFIG_RANDOMIZE_MEMORY into account in kaslr_enabled()]
  Link: http://lkml.kernel.org/r/20200525104045.GB13212@linux.ibm.com



Signed-off-by: default avatarMike Rapoport <rppt@linux.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Cain <bcain@codeaurora.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Cc: Guan Xuetao <gxt@pku.edu.cn>
Cc: Guo Ren <guoren@kernel.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ley Foon Tan <ley.foon.tan@intel.com>
Cc: Mark Salter <msalter@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Nick Hu <nickhu@andestech.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Rich Felker <dalias@libc.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Vincent Chen <deanbo422@gmail.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Link: http://lkml.kernel.org/r/20200514170327.31389-8-rppt@kernel.org


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1bcdc68d

arch/x86/include/asm/kaslr.h

+2 −0
Original line number Diff line number Diff line
@@ -6,8 +6,10 @@ unsigned long kaslr_get_random_long(const char *purpose); 


#ifdef CONFIG_RANDOMIZE_MEMORY

void kernel_randomize_memory(void);

void init_trampoline_kaslr(void);

#else

static inline void kernel_randomize_memory(void) { }

static inline void init_trampoline_kaslr(void) {}

#endif /* CONFIG_RANDOMIZE_MEMORY */



#endif

arch/x86/include/asm/pgtable.h

+1 −14
Original line number Diff line number Diff line
@@ -1071,27 +1071,14 @@ void init_mem_mapping(void); 
void early_alloc_pgt_buf(void);

extern void memblock_find_dma_reserve(void);





#ifdef CONFIG_X86_64

/* Realmode trampoline initialization. */

extern pgd_t trampoline_pgd_entry;

static inline void __meminit init_trampoline_default(void)

{

	/* Default trampoline pgd value */

	trampoline_pgd_entry = init_top_pgt[pgd_index(__PAGE_OFFSET)];

}



void __init poking_init(void);



unsigned long init_memory_mapping(unsigned long start,

				  unsigned long end, pgprot_t prot);



# ifdef CONFIG_RANDOMIZE_MEMORY

void __meminit init_trampoline(void);

# else

#  define init_trampoline init_trampoline_default

# endif

#else

static inline void init_trampoline(void) { }

#endif



/* local pte updates need not use xchg for locking */

arch/x86/include/asm/setup.h

+11 −1
Original line number Diff line number Diff line
@@ -75,7 +75,17 @@ extern char _text[]; 


static inline bool kaslr_enabled(void)

{

	return !!(boot_params.hdr.loadflags & KASLR_FLAG);

	return IS_ENABLED(CONFIG_RANDOMIZE_MEMORY) &&

		!!(boot_params.hdr.loadflags & KASLR_FLAG);

}



/*

 * Apply no randomization if KASLR was disabled at boot or if KASAN

 * is enabled. KASAN shadow mappings rely on regions being PGD aligned.

 */

static inline bool kaslr_memory_enabled(void)

{

	return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);

}



static inline unsigned long kaslr_offset(void)

arch/x86/mm/init.c

+22 −0
Original line number Diff line number Diff line
@@ -680,6 +680,28 @@ static void __init memory_map_bottom_up(unsigned long map_start, 
	}

}



/*

 * The real mode trampoline, which is required for bootstrapping CPUs

 * occupies only a small area under the low 1MB.  See reserve_real_mode()

 * for details.

 *

 * If KASLR is disabled the first PGD entry of the direct mapping is copied

 * to map the real mode trampoline.

 *

 * If KASLR is enabled, copy only the PUD which covers the low 1MB

 * area. This limits the randomization granularity to 1GB for both 4-level

 * and 5-level paging.

 */

static void __init init_trampoline(void)

{

#ifdef CONFIG_X86_64

	if (!kaslr_memory_enabled())

		trampoline_pgd_entry = init_top_pgt[pgd_index(__PAGE_OFFSET)];

	else

		init_trampoline_kaslr();

#endif

}



void __init init_mem_mapping(void)

{

	unsigned long end;

arch/x86/mm/kaslr.c

+1 −32
Original line number Diff line number Diff line
@@ -61,15 +61,6 @@ static inline unsigned long get_padding(struct kaslr_memory_region *region) 
	return (region->size_tb << TB_SHIFT);

}



/*

 * Apply no randomization if KASLR was disabled at boot or if KASAN

 * is enabled. KASAN shadow mappings rely on regions being PGD aligned.

 */

static inline bool kaslr_memory_enabled(void)

{

	return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);

}



/* Initialize base and padding for each memory region randomized with KASLR */

void __init kernel_randomize_memory(void)

{
@@ -148,7 +139,7 @@ void __init kernel_randomize_memory(void) 
	}

}



static void __meminit init_trampoline_pud(void)

void __meminit init_trampoline_kaslr(void)

{

	pud_t *pud_page_tramp, *pud, *pud_tramp;

	p4d_t *p4d_page_tramp, *p4d, *p4d_tramp;
@@ -189,25 +180,3 @@ static void __meminit init_trampoline_pud(void) 
			__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));

	}

}
 


/*

 * The real mode trampoline, which is required for bootstrapping CPUs

 * occupies only a small area under the low 1MB.  See reserve_real_mode()

 * for details.

 *

 * If KASLR is disabled the first PGD entry of the direct mapping is copied

 * to map the real mode trampoline.

 *

 * If KASLR is enabled, copy only the PUD which covers the low 1MB

 * area. This limits the randomization granularity to 1GB for both 4-level

 * and 5-level paging.

 */

void __meminit init_trampoline(void)

{

	if (!kaslr_memory_enabled()) {

		init_trampoline_default();

		return;

	}



	init_trampoline_pud();

}

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