Re: [PATCH] kvm-s390: fix potential array overrun in intercept handling

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On 01/21/2010 12:56 PM, Christian Borntraeger wrote:
Avi, Marcelo,

kvm_handle_sie_intercept uses a jump table to get the intercept handler
for a SIE intercept. Static code analysis revealed a potential problem:
the intercept_funcs jump table was defined to contain (0x48>>  2) entries,
but we only checked for code>  0x48 which would cause an off-by-one
array overflow if code == 0x48.

Since the table is only populated up to (0x28>>  2), we can reduce the
jump table size while fixing the off-by-one.



-static const intercept_handler_t intercept_funcs[0x48>>  2] = {
+static const intercept_handler_t intercept_funcs[(0x28>>  2) + 1] = {
  	[0x00>>  2] = handle_noop,
  	[0x04>>  2] = handle_instruction,
  	[0x08>>  2] = handle_prog,
  	[0x0C>>  2] = handle_instruction_and_prog,
  	[0x10>>  2] = handle_noop,
  	[0x14>>  2] = handle_noop,
  	[0x1C>>  2] = kvm_s390_handle_wait,
  	[0x20>>  2] = handle_validity,
  	[0x28>>  2] = handle_stop,
  };

You can define the array without a size to let the compiler figure out the minimum size.


  int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
  {
  	intercept_handler_t func;
  	u8 code = vcpu->arch.sie_block->icptcode;

-	if (code&  3 || code>  0x48)
+	if (code&  3 || code>  0x28)
  		return -ENOTSUPP;

And here, check against ARRAY_SIZE() instead of a magic number.


--
error compiling committee.c: too many arguments to function

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