On 06/23/2014 10:44 AM, David Laight wrote: > From: Markos Chandras >> Remove BUG_ON() if the shift immediate is >=32 to avoid >> kernel crashes due to malicious user input. Since the micro-assembler >> will not allow an immediate greater or equal to 32, we will use the >> maximum value which is 31. This will do the correct thing on either 32- >> or 64-bit cores since no 64-bit instructions are being used in JIT. > > I'm not sure that bounding the shift to 31 bits 'is the correct thing'. > I'd have thought that emulating the large shift or masking the shift > to 5 bits are equally 'correct'. > > ... Hi David, Since we use 32-bit registers (or rather, we ignore the top 32bits on MIPS64), shifting >= 32 will always result to 0. Alexei suggested [1] to allow large shifts and emulate them, so this patch aims to do that by treating >=32 shift values as 31. Please tell me if I got this wrong. [1] http://www.linux-mips.org/archives/linux-mips/2014-06/msg00212.html -- markos
