H. Peter Anvin wrote: > Philipp Kohlbecher wrote: >> From: Philipp Kohlbecher <[EMAIL PROTECTED]> >> >> 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 don't know of any problems this causes. The kernel needs to be aware of the fact that the xss and esp fields of the pt_regs struct may contain wrong values anyway, as hardware interrupts arriving while the CPU is in kernel mode would also lead to this condition. The file include/asm-i386/processor.h contains a comment to that effect (lines 483-492). With kernel_execve we can predict this, however, and account for it. (This may be superfluous, but I don't think it hurts and it might prevent future errors.) - Phil Kohlbecher - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
