Commit 1dbf527c authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Andi Kleen
Browse files

[PATCH] i386: Make COMPAT_VDSO runtime selectable. 



Now that relocation of the VDSO for COMPAT_VDSO users is done at
runtime rather than compile time, it is possible to enable/disable
compat mode at runtime.

This patch allows you to enable COMPAT_VDSO mode with "vdso=2" on the
kernel command line, or via sysctl.  (Switching on a running system
shouldn't be done lightly; any process which was relying on the compat
VDSO will be upset if it goes away.)

The COMPAT_VDSO config option still exists, but if enabled it just
makes vdso_enabled default to VDSO_COMPAT.

+From: Hugh Dickins <hugh@veritas.com>

Fix oops from i386-make-compat_vdso-runtime-selectable.patch.

Even mingetty at system startup finds it easy to trigger an oops
while reading /proc/PID/maps: though it has a good hold on the mm
itself, that cannot stop exit_mm() from resetting tsk->mm to NULL.

(It is usually show_map()'s call to get_gate_vma() which oopses,
and I expect we could change that to check priv->tail_vma instead;
but no matter, even m_start()'s call just after get_task_mm() is racy.)

Signed-off-by: default avatarJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Cc: Zachary Amsden <zach@vmware.com>
Cc: "Jan Beulich" <JBeulich@novell.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Roland McGrath <roland@redhat.com>
parent d4f7a2c1

Documentation/kernel-parameters.txt

+1 −0
Original line number Diff line number Diff line
@@ -1820,6 +1820,7 @@ and is between 256 and 4096 characters. It is defined in the file 
			[USBHID] The interval which mice are to be polled at.



	vdso=		[IA-32,SH]

			vdso=2: enable compat VDSO (default with COMPAT_VDSO)

			vdso=1: enable VDSO (default)

			vdso=0: disable VDSO mapping

arch/i386/kernel/sysenter.c

+94 −51
Original line number Diff line number Diff line
@@ -23,16 +23,25 @@ 
#include <asm/pgtable.h>

#include <asm/unistd.h>

#include <asm/elf.h>

#include <asm/tlbflush.h>



enum {

	VDSO_DISABLED = 0,

	VDSO_ENABLED = 1,

	VDSO_COMPAT = 2,

};



#ifdef CONFIG_COMPAT_VDSO

#define VDSO_DEFAULT	VDSO_COMPAT

#else

#define VDSO_DEFAULT	VDSO_ENABLED

#endif



/*

 * Should the kernel map a VDSO page into processes and pass its

 * address down to glibc upon exec()?

 */

#ifdef CONFIG_PARAVIRT

unsigned int __read_mostly vdso_enabled = 0;

#else

unsigned int __read_mostly vdso_enabled = 1;

#endif

unsigned int __read_mostly vdso_enabled = VDSO_DEFAULT;



EXPORT_SYMBOL_GPL(vdso_enabled);
@@ -47,7 +56,6 @@ __setup("vdso=", vdso_setup); 


extern asmlinkage void sysenter_entry(void);



#ifdef CONFIG_COMPAT_VDSO

static __init void reloc_symtab(Elf32_Ehdr *ehdr,

				unsigned offset, unsigned size)

{
@@ -164,11 +172,6 @@ static __init void relocate_vdso(Elf32_Ehdr *ehdr) 
				     shdr[i].sh_size);

	}

}

#else

static inline void relocate_vdso(Elf32_Ehdr *ehdr)

{

}

#endif	/* COMPAT_VDSO */



void enable_sep_cpu(void)

{
@@ -188,6 +191,25 @@ void enable_sep_cpu(void) 
	put_cpu();	

}



static struct vm_area_struct gate_vma;



static int __init gate_vma_init(void)

{

	gate_vma.vm_mm = NULL;

	gate_vma.vm_start = FIXADDR_USER_START;

	gate_vma.vm_end = FIXADDR_USER_END;

	gate_vma.vm_flags = VM_READ | VM_MAYREAD | VM_EXEC | VM_MAYEXEC;

	gate_vma.vm_page_prot = __P101;

	/*

	 * Make sure the vDSO gets into every core dump.

	 * Dumping its contents makes post-mortem fully interpretable later

	 * without matching up the same kernel and hardware config to see

	 * what PC values meant.

	 */

	gate_vma.vm_flags |= VM_ALWAYSDUMP;

	return 0;

}



/*

 * These symbols are defined by vsyscall.o to mark the bounds

 * of the ELF DSO images included therein.
@@ -196,6 +218,22 @@ extern const char vsyscall_int80_start, vsyscall_int80_end; 
extern const char vsyscall_sysenter_start, vsyscall_sysenter_end;

static struct page *syscall_pages[1];



static void map_compat_vdso(int map)

{

	static int vdso_mapped;



	if (map == vdso_mapped)

		return;



	vdso_mapped = map;



	__set_fixmap(FIX_VDSO, page_to_pfn(syscall_pages[0]) << PAGE_SHIFT,

		     map ? PAGE_READONLY_EXEC : PAGE_NONE);



	/* flush stray tlbs */

	flush_tlb_all();

}



int __init sysenter_setup(void)

{

	void *syscall_page = (void *)get_zeroed_page(GFP_ATOMIC);
@@ -204,10 +242,9 @@ int __init sysenter_setup(void) 


	syscall_pages[0] = virt_to_page(syscall_page);



#ifdef CONFIG_COMPAT_VDSO

	__set_fixmap(FIX_VDSO, __pa(syscall_page), PAGE_READONLY_EXEC);

	gate_vma_init();



	printk("Compat vDSO mapped to %08lx.\n", __fix_to_virt(FIX_VDSO));

#endif



	if (!boot_cpu_has(X86_FEATURE_SEP)) {

		vsyscall = &vsyscall_int80_start;
@@ -226,15 +263,25 @@ int __init sysenter_setup(void) 
/* Defined in vsyscall-sysenter.S */

extern void SYSENTER_RETURN;



#ifdef __HAVE_ARCH_GATE_AREA

/* Setup a VMA at program startup for the vsyscall page */

int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)

{

	struct mm_struct *mm = current->mm;

	unsigned long addr;

	int ret;

	bool compat;



	down_write(&mm->mmap_sem);



	/* Test compat mode once here, in case someone

	   changes it via sysctl */

	compat = (vdso_enabled == VDSO_COMPAT);



	map_compat_vdso(compat);



	if (compat)

		addr = VDSO_HIGH_BASE;

	else {

		addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);

		if (IS_ERR_VALUE(addr)) {

			ret = addr;
@@ -245,23 +292,28 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack) 
		 * MAYWRITE to allow gdb to COW and set breakpoints

		 *

		 * Make sure the vDSO gets into every core dump.

	 * Dumping its contents makes post-mortem fully interpretable later

	 * without matching up the same kernel and hardware config to see

	 * what PC values meant.

		 * Dumping its contents makes post-mortem fully

		 * interpretable later without matching up the same

		 * kernel and hardware config to see what PC values

		 * meant.

		 */

		ret = install_special_mapping(mm, addr, PAGE_SIZE,

					      VM_READ|VM_EXEC|

					      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|

					      VM_ALWAYSDUMP,

					      syscall_pages);



		if (ret)

			goto up_fail;

	}



	current->mm->context.vdso = (void *)addr;

	current_thread_info()->sysenter_return =

		(void *)VDSO_SYM(&SYSENTER_RETURN);



  up_fail:

	up_write(&mm->mmap_sem);



	return ret;

}
@@ -274,6 +326,11 @@ const char *arch_vma_name(struct vm_area_struct *vma) 


struct vm_area_struct *get_gate_vma(struct task_struct *tsk)

{

	struct mm_struct *mm = tsk->mm;



	/* Check to see if this task was created in compat vdso mode */

	if (mm && mm->context.vdso == (void *)VDSO_HIGH_BASE)

		return &gate_vma;

	return NULL;

}
@@ -286,17 +343,3 @@ int in_gate_area_no_task(unsigned long addr) 
{

	return 0;

}
 
#else  /* !__HAVE_ARCH_GATE_AREA */

int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)

{

	/*

	 * If not creating userspace VMA, simply set vdso to point to

	 * fixmap page.

	 */

	current->mm->context.vdso = (void *)VDSO_HIGH_BASE;

	current_thread_info()->sysenter_return =

		(void *)VDSO_SYM(&SYSENTER_RETURN);



	return 0;

}

#endif	/* __HAVE_ARCH_GATE_AREA */

include/asm-i386/page.h

+0 −2
Original line number Diff line number Diff line
@@ -143,9 +143,7 @@ extern int page_is_ram(unsigned long pagenr); 
#include <asm-generic/memory_model.h>

#include <asm-generic/page.h>



#ifndef CONFIG_COMPAT_VDSO

#define __HAVE_ARCH_GATE_AREA 1

#endif

#endif /* __KERNEL__ */



#endif /* _I386_PAGE_H */

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