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

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Message-ID: <464CD44A.5000307@zytor.com>
Date:	Thu, 17 May 2007 15:16:42 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Philipp Kohlbecher <pk031698@...-greifswald.de>
CC:	Dave Jones <davej@...emonkey.org.uk>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	linux-assembly@...r.kernel.org
Subject: Re: [PATCH 2.6.21.1] i386: save registers before intra-privilege
 syscall

Philipp Kohlbecher wrote:
> From: Philipp Kohlbecher <pk031698@...-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
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