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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: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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parent
f43bb27ebf
commit
8f5ca0b319
1 changed files with 48 additions and 36 deletions
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@ -71,15 +71,15 @@ static inline bool notify_page_fault(struct pt_regs *regs)
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* Check whether the instruction at regs->nip is a store using
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* an update addressing form which will update r1.
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*/
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static int store_updates_sp(struct pt_regs *regs)
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static bool store_updates_sp(struct pt_regs *regs)
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{
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unsigned int inst;
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if (get_user(inst, (unsigned int __user *)regs->nip))
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return 0;
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return false;
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/* check for 1 in the rA field */
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if (((inst >> 16) & 0x1f) != 1)
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return 0;
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return false;
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/* check major opcode */
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switch (inst >> 26) {
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case 37: /* stwu */
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@ -87,7 +87,7 @@ static int store_updates_sp(struct pt_regs *regs)
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case 45: /* sthu */
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case 53: /* stfsu */
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case 55: /* stfdu */
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return 1;
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return true;
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case 62: /* std or stdu */
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return (inst & 3) == 1;
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case 31:
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@ -99,10 +99,10 @@ static int store_updates_sp(struct pt_regs *regs)
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case 439: /* sthux */
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case 695: /* stfsux */
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case 759: /* stfdux */
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return 1;
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return true;
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}
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}
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return 0;
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return false;
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}
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/*
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* do_page_fault error handling helpers
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@ -222,6 +222,43 @@ static bool bad_kernel_fault(bool is_exec, unsigned long error_code,
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return is_exec || (address >= TASK_SIZE);
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}
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static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
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struct vm_area_struct *vma,
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bool store_update_sp)
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{
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/*
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* N.B. The POWER/Open ABI allows programs to access up to
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* 288 bytes below the stack pointer.
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* The kernel signal delivery code writes up to about 1.5kB
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* below the stack pointer (r1) before decrementing it.
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* The exec code can write slightly over 640kB to the stack
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* before setting the user r1. Thus we allow the stack to
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* expand to 1MB without further checks.
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*/
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if (address + 0x100000 < vma->vm_end) {
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/* get user regs even if this fault is in kernel mode */
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struct pt_regs *uregs = current->thread.regs;
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if (uregs == NULL)
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return true;
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/*
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* A user-mode access to an address a long way below
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* the stack pointer is only valid if the instruction
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* is one which would update the stack pointer to the
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* address accessed if the instruction completed,
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* i.e. either stwu rs,n(r1) or stwux rs,r1,rb
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* (or the byte, halfword, float or double forms).
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*
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* If we don't check this then any write to the area
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* between the last mapped region and the stack will
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* expand the stack rather than segfaulting.
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*/
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if (address + 2048 < uregs->gpr[1] && !store_update_sp)
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return true;
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}
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return false;
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}
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static bool access_error(bool is_write, bool is_exec,
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struct vm_area_struct *vma)
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{
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@ -350,7 +387,7 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
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int is_user = user_mode(regs);
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int is_write = page_fault_is_write(error_code);
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int fault, major = 0;
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int store_update_sp = 0;
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bool store_update_sp = false;
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#ifdef CONFIG_PPC_ICSWX
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/*
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@ -458,36 +495,11 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
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if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
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return bad_area(regs, address);
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/*
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* N.B. The POWER/Open ABI allows programs to access up to
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* 288 bytes below the stack pointer.
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* The kernel signal delivery code writes up to about 1.5kB
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* below the stack pointer (r1) before decrementing it.
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* The exec code can write slightly over 640kB to the stack
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* before setting the user r1. Thus we allow the stack to
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* expand to 1MB without further checks.
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*/
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if (address + 0x100000 < vma->vm_end) {
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/* get user regs even if this fault is in kernel mode */
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struct pt_regs *uregs = current->thread.regs;
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if (uregs == NULL)
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/* The stack is being expanded, check if it's valid */
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if (unlikely(bad_stack_expansion(regs, address, vma, store_update_sp)))
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return bad_area(regs, address);
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/*
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* A user-mode access to an address a long way below
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* the stack pointer is only valid if the instruction
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* is one which would update the stack pointer to the
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* address accessed if the instruction completed,
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* i.e. either stwu rs,n(r1) or stwux rs,r1,rb
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* (or the byte, halfword, float or double forms).
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*
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* If we don't check this then any write to the area
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* between the last mapped region and the stack will
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* expand the stack rather than segfaulting.
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*/
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if (address + 2048 < uregs->gpr[1] && !store_update_sp)
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return bad_area(regs, address);
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}
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/* Try to expand it */
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if (unlikely(expand_stack(vma, address)))
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return bad_area(regs, address);
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