Re: [PATCH 2.6.21.1] i386: save registers before intra-privilege syscall

["H. Peter Anvin" <hpa@zytor.com>]

Philipp Kohlbecher wrote:
> From: Philipp Kohlbecher <pk031698@uni-greifswald.de>
> 
> The kernel_execve function issues a software interrupt (int 0x80) to make
> a system call to sys_execve. This function expects to find the stack segment
> and stack pointer of the function that issued the system call in the pt_regs
> struct. The syscall entry code that sets up this struct expects the stack
> segment and the stack pointer of the issuing function already on the stack.
> But the Intel processor saves these registers only if a stack-switch occurs,
> i.e. for inter-privilege interrupts and exceptions (cf. Intel Software
> Developer’s Manual, Vol. 3A, p. 5-17,
> http://www.intel.com/design/processor/manuals/253668.pdf).
> For an intra-privilege interrupt like the one issued in kernel_execve, these
> registers must be saved manually.
> 

Could you describe the failure scenario this causes?  I'm trying to
understand how something that fundamental would have possibly slipped by
testing?

	-hpa