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Commit 8f5ca0b3 authored by Benjamin Herrenschmidt's avatar Benjamin Herrenschmidt Committed by Michael Ellerman
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powerpc/mm: Cleanup check for stack expansion 



When hitting below a VM_GROWSDOWN vma (typically growing the stack),
we check whether it's a valid stack-growing instruction and we
check the distance to GPR1. This is largely open coded with lots
of comments, so move it out to a helper.

While at it, make store_update_sp a boolean.

Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent f43bb27e

arch/powerpc/mm/fault.c

+48 −36
Original line number Diff line number Diff line
@@ -71,15 +71,15 @@ static inline bool notify_page_fault(struct pt_regs *regs) 
 * Check whether the instruction at regs->nip is a store using

 * an update addressing form which will update r1.

 */

static int store_updates_sp(struct pt_regs *regs)

static bool store_updates_sp(struct pt_regs *regs)

{

	unsigned int inst;



	if (get_user(inst, (unsigned int __user *)regs->nip))

		return 0;

		return false;

	/* check for 1 in the rA field */

	if (((inst >> 16) & 0x1f) != 1)

		return 0;

		return false;

	/* check major opcode */

	switch (inst >> 26) {

	case 37:	/* stwu */
@@ -87,7 +87,7 @@ static int store_updates_sp(struct pt_regs *regs) 
	case 45:	/* sthu */

	case 53:	/* stfsu */

	case 55:	/* stfdu */

		return 1;

		return true;

	case 62:	/* std or stdu */

		return (inst & 3) == 1;

	case 31:
@@ -99,10 +99,10 @@ static int store_updates_sp(struct pt_regs *regs) 
		case 439:	/* sthux */

		case 695:	/* stfsux */

		case 759:	/* stfdux */

			return 1;

			return true;

		}

	}

	return 0;

	return false;

}

/*

 * do_page_fault error handling helpers
@@ -222,6 +222,43 @@ static bool bad_kernel_fault(bool is_exec, unsigned long error_code, 
	return is_exec || (address >= TASK_SIZE);

}



static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,

				struct vm_area_struct *vma,

				bool store_update_sp)

{

	/*

	 * N.B. The POWER/Open ABI allows programs to access up to

	 * 288 bytes below the stack pointer.

	 * The kernel signal delivery code writes up to about 1.5kB

	 * below the stack pointer (r1) before decrementing it.

	 * The exec code can write slightly over 640kB to the stack

	 * before setting the user r1.  Thus we allow the stack to

	 * expand to 1MB without further checks.

	 */

	if (address + 0x100000 < vma->vm_end) {

		/* get user regs even if this fault is in kernel mode */

		struct pt_regs *uregs = current->thread.regs;

		if (uregs == NULL)

			return true;



		/*

		 * A user-mode access to an address a long way below

		 * the stack pointer is only valid if the instruction

		 * is one which would update the stack pointer to the

		 * address accessed if the instruction completed,

		 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb

		 * (or the byte, halfword, float or double forms).

		 *

		 * If we don't check this then any write to the area

		 * between the last mapped region and the stack will

		 * expand the stack rather than segfaulting.

		 */

		if (address + 2048 < uregs->gpr[1] && !store_update_sp)

			return true;

	}

	return false;

}



static bool access_error(bool is_write, bool is_exec,

			 struct vm_area_struct *vma)

{
@@ -350,7 +387,7 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address, 
	int is_user = user_mode(regs);

	int is_write = page_fault_is_write(error_code);

	int fault, major = 0;

	int store_update_sp = 0;

	bool store_update_sp = false;



#ifdef CONFIG_PPC_ICSWX

	/*
@@ -458,36 +495,11 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address, 
	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))

		return bad_area(regs, address);



	/*

	 * N.B. The POWER/Open ABI allows programs to access up to

	 * 288 bytes below the stack pointer.

	 * The kernel signal delivery code writes up to about 1.5kB

	 * below the stack pointer (r1) before decrementing it.

	 * The exec code can write slightly over 640kB to the stack

	 * before setting the user r1.  Thus we allow the stack to

	 * expand to 1MB without further checks.

	 */

	if (address + 0x100000 < vma->vm_end) {

		/* get user regs even if this fault is in kernel mode */

		struct pt_regs *uregs = current->thread.regs;

		if (uregs == NULL)

	/* The stack is being expanded, check if it's valid */

	if (unlikely(bad_stack_expansion(regs, address, vma, store_update_sp)))

		return bad_area(regs, address);



		/*

		 * A user-mode access to an address a long way below

		 * the stack pointer is only valid if the instruction

		 * is one which would update the stack pointer to the

		 * address accessed if the instruction completed,

		 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb

		 * (or the byte, halfword, float or double forms).

		 *

		 * If we don't check this then any write to the area

		 * between the last mapped region and the stack will

		 * expand the stack rather than segfaulting.

		 */

		if (address + 2048 < uregs->gpr[1] && !store_update_sp)

			return bad_area(regs, address);

	}

	/* Try to expand it */

	if (unlikely(expand_stack(vma, address)))

		return bad_area(regs, address);