Alex Smith e90e6fddc5 MIPS: O32/32-bit: Fix bug which can cause incorrect system call restarts ... On 32-bit/O32, pt_regs has a padding area at the beginning into which the syscall arguments passed via the user stack are copied. 4 arguments totalling 16 bytes are copied to offset 16 bytes into this area, however the area is only 24 bytes long. This means the last 2 arguments overwrite pt_regs->regs[{0,1}]. If a syscall function returns an error, handle_sys stores the original syscall number in pt_regs->regs[0] for syscall restart. signal.c checks whether regs[0] is non-zero, if it is it will check whether the syscall return value is one of the ERESTART* codes to see if it must be restarted. Should a syscall be made that results in a non-zero value being copied off the user stack into regs[0], and then returns a positive (non-error) value that matches one of the ERESTART* error codes, this can be mistaken for requiring a syscall restart. While the possibility for this to occur has always existed, it is made much more likely to occur by commit 46e12c07b3 ("MIPS: O32 / 32-bit: Always copy 4 stack arguments."), since now every syscall will copy 4 arguments and overwrite regs[0], rather than just those with 7 or 8 arguments. Since that commit, booting Debian under a 32-bit MIPS kernel almost always results in a hang early in boot, due to a wait4 syscall returning a PID that matches one of the ERESTART* codes, which then causes an incorrect restart of the syscall. The problem is fixed by increasing the size of the padding area so that arguments copied off the stack will not overwrite pt_regs->regs[{0,1}]. Signed-off-by: Alex Smith <alex.smith@imgtec.com> Cc: <stable@vger.kernel.org> # v3.13+ Reviewed-by: Aurelien Jarno <aurelien@aurel32.net> Tested-by: Aurelien Jarno <aurelien@aurel32.net> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/7454/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>		2014-08-02 00:06:37 +02:00
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asm	MIPS: O32/32-bit: Fix bug which can cause incorrect system call restarts	2014-08-02 00:06:37 +02:00
uapi/asm	MIPS: uasm: Add SLT uasm instruction	2014-06-26 10:48:19 +01:00