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powerpc/mm: Cleanup check for stack expansion

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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: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Benjamin Herrenschmidt 2017-07-19 14:49:45 +10:00 committed by Michael Ellerman
parent f43bb27ebf
commit 8f5ca0b319
1 changed files with 48 additions and 36 deletions
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82
arch/powerpc/mm/fault.c
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@ -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);