Commit e47690d7 authored by Steven Price's avatar Steven Price Committed by Linus Torvalds
Browse files

x86: mm: avoid allocating struct mm_struct on the stack 

struct mm_struct is quite large (~1664 bytes) and so allocating on the
stack may cause problems as the kernel stack size is small.

Since ptdump_walk_pgd_level_core() was only allocating the structure so
that it could modify the pgd argument we can instead introduce a pgd
override in struct mm_walk and pass this down the call stack to where it
is needed.

Since the correct mm_struct is now being passed down, it is now also
unnecessary to take the mmap_sem semaphore because ptdump_walk_pgd() will
now take the semaphore on the real mm.

[steven.price@arm.com: restore missed arm64 changes]
  Link: http://lkml.kernel.org/r/20200108145710.34314-1-steven.price@arm.com
Link: http://lkml.kernel.org/r/20200108145710.34314-1-steven.price@arm.com


Signed-off-by: default avatarSteven Price <steven.price@arm.com>
Reported-by: default avatarStephen Rothwell <sfr@canb.auug.org.au>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: "Liang, Kan" <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zong Li <zong.li@sifive.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f8f0d0b6

arch/arm64/mm/dump.c

+2 −2
Original line number Diff line number Diff line
@@ -323,7 +323,7 @@ void ptdump_walk(struct seq_file *s, struct ptdump_info *info) 
		}

	};



	ptdump_walk_pgd(&st.ptdump, info->mm);

	ptdump_walk_pgd(&st.ptdump, info->mm, NULL);

}



static void ptdump_initialize(void)
@@ -361,7 +361,7 @@ void ptdump_check_wx(void) 
		}

	};



	ptdump_walk_pgd(&st.ptdump, &init_mm);

	ptdump_walk_pgd(&st.ptdump, &init_mm, NULL);



	if (st.wx_pages || st.uxn_pages)

		pr_warn("Checked W+X mappings: FAILED, %lu W+X pages found, %lu non-UXN pages found\n",

arch/x86/mm/debug_pagetables.c

+2 −8
Original line number Diff line number Diff line
@@ -15,11 +15,8 @@ DEFINE_SHOW_ATTRIBUTE(ptdump); 


static int ptdump_curknl_show(struct seq_file *m, void *v)

{

	if (current->mm->pgd) {

		down_read(&current->mm->mmap_sem);

	if (current->mm->pgd)

		ptdump_walk_pgd_level_debugfs(m, current->mm, false);

		up_read(&current->mm->mmap_sem);

	}

	return 0;

}
@@ -28,11 +25,8 @@ DEFINE_SHOW_ATTRIBUTE(ptdump_curknl); 
#ifdef CONFIG_PAGE_TABLE_ISOLATION

static int ptdump_curusr_show(struct seq_file *m, void *v)

{

	if (current->mm->pgd) {

		down_read(&current->mm->mmap_sem);

	if (current->mm->pgd)

		ptdump_walk_pgd_level_debugfs(m, current->mm, true);

		up_read(&current->mm->mmap_sem);

	}

	return 0;

}

arch/x86/mm/dump_pagetables.c

+7 −11
Original line number Diff line number Diff line
@@ -357,7 +357,8 @@ static void note_page(struct ptdump_state *pt_st, unsigned long addr, int level, 
	}

}



static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,

static void ptdump_walk_pgd_level_core(struct seq_file *m,

				       struct mm_struct *mm, pgd_t *pgd,

				       bool checkwx, bool dmesg)

{

	const struct ptdump_range ptdump_ranges[] = {
@@ -386,12 +387,7 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd, 
		.seq		= m

	};



	struct mm_struct fake_mm = {

		.pgd = pgd

	};

	init_rwsem(&fake_mm.mmap_sem);



	ptdump_walk_pgd(&st.ptdump, &fake_mm);

	ptdump_walk_pgd(&st.ptdump, mm, pgd);



	if (!checkwx)

		return;
@@ -404,7 +400,7 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd, 


void ptdump_walk_pgd_level(struct seq_file *m, struct mm_struct *mm)

{

	ptdump_walk_pgd_level_core(m, mm->pgd, false, true);

	ptdump_walk_pgd_level_core(m, mm, mm->pgd, false, true);

}



void ptdump_walk_pgd_level_debugfs(struct seq_file *m, struct mm_struct *mm,
@@ -415,7 +411,7 @@ void ptdump_walk_pgd_level_debugfs(struct seq_file *m, struct mm_struct *mm, 
	if (user && boot_cpu_has(X86_FEATURE_PTI))

		pgd = kernel_to_user_pgdp(pgd);

#endif

	ptdump_walk_pgd_level_core(m, pgd, false, false);

	ptdump_walk_pgd_level_core(m, mm, pgd, false, false);

}

EXPORT_SYMBOL_GPL(ptdump_walk_pgd_level_debugfs);
@@ -430,13 +426,13 @@ void ptdump_walk_user_pgd_level_checkwx(void) 


	pr_info("x86/mm: Checking user space page tables\n");

	pgd = kernel_to_user_pgdp(pgd);

	ptdump_walk_pgd_level_core(NULL, pgd, true, false);

	ptdump_walk_pgd_level_core(NULL, &init_mm, pgd, true, false);

#endif

}



void ptdump_walk_pgd_level_checkwx(void)

{

	ptdump_walk_pgd_level_core(NULL, INIT_PGD, true, false);

	ptdump_walk_pgd_level_core(NULL, &init_mm, INIT_PGD, true, false);

}



static int __init pt_dump_init(void)

include/linux/pagewalk.h

+3 −0
Original line number Diff line number Diff line
@@ -74,6 +74,7 @@ enum page_walk_action { 
 * mm_walk - walk_page_range data

 * @ops:	operation to call during the walk

 * @mm:		mm_struct representing the target process of page table walk

 * @pgd:	pointer to PGD; only valid with no_vma (otherwise set to NULL)

 * @vma:	vma currently walked (NULL if walking outside vmas)

 * @action:	next action to perform (see enum page_walk_action)

 * @no_vma:	walk ignoring vmas (vma will always be NULL)
@@ -84,6 +85,7 @@ enum page_walk_action { 
struct mm_walk {

	const struct mm_walk_ops *ops;

	struct mm_struct *mm;

	pgd_t *pgd;

	struct vm_area_struct *vma;

	enum page_walk_action action;

	bool no_vma;
@@ -95,6 +97,7 @@ int walk_page_range(struct mm_struct *mm, unsigned long start, 
		void *private);

int walk_page_range_novma(struct mm_struct *mm, unsigned long start,

			  unsigned long end, const struct mm_walk_ops *ops,

			  pgd_t *pgd,

			  void *private);

int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,

		void *private);

include/linux/ptdump.h

+1 −1
Original line number Diff line number Diff line
@@ -17,6 +17,6 @@ struct ptdump_state { 
	const struct ptdump_range *range;

};



void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm);

void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd);



#endif /* _LINUX_PTDUMP_H */

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