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Commit 0998e422 authored by Zachary Amsden's avatar Zachary Amsden Committed by Linus Torvalds
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[PATCH] x86: privilege cleanup 



Privilege checking cleanup.  Originally, these diffs were much greater, but
recent cleanups in Linux have already done much of the cleanup.  I added
some explanatory comments in places where the reasoning behind certain
tests is rather subtle.

Also, in traps.c, we can skip the user_mode check in handle_BUG().  The
reason is, there are only two call chains - one via die_if_kernel() and one
via do_page_fault(), both entering from die().  Both of these paths already
ensure that a kernel mode failure has happened.  Also, the original check
here, if (user_mode(regs)) was insufficient anyways, since it would not
rule out BUG faults from V8086 mode execution.

Saving the %ss segment in show_regs() rather than assuming a fixed value
also gives better information about the current kernel state in the
register dump.

Signed-off-by: default avatarZachary Amsden <zach@vmware.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent f2ab4461

arch/i386/kernel/signal.c

+3 −1
Original line number Diff line number Diff line
@@ -604,7 +604,9 @@ int fastcall do_signal(struct pt_regs *regs, sigset_t *oldset) 
	 * We want the common case to go fast, which

	 * is why we may in certain cases get here from

	 * kernel mode. Just return without doing anything

	 * if so.

 	 * if so.  vm86 regs switched out by assembly code

 	 * before reaching here, so testing against kernel

 	 * CS suffices.

	 */

	if (!user_mode(regs))

		return 1;

arch/i386/kernel/traps.c

+1 −4
Original line number Diff line number Diff line
@@ -210,7 +210,7 @@ void show_registers(struct pt_regs *regs) 
	unsigned short ss;



	esp = (unsigned long) (&regs->esp);

	ss = __KERNEL_DS;

	savesegment(ss, ss);

	if (user_mode(regs)) {

		in_kernel = 0;

		esp = regs->esp;
@@ -267,9 +267,6 @@ static void handle_BUG(struct pt_regs *regs) 
	char c;

	unsigned long eip;



	if (user_mode(regs))

		goto no_bug;		/* Not in kernel */



	eip = regs->eip;



	if (eip < PAGE_OFFSET)

include/asm-i386/ptrace.h

+7 −0
Original line number Diff line number Diff line
@@ -61,6 +61,13 @@ struct pt_regs { 
struct task_struct;

extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code);



/*

 * user_mode_vm(regs) determines whether a register set came from user mode.

 * This is true if V8086 mode was enabled OR if the register set was from

 * protected mode with RPL-3 CS value.  This tricky test checks that with

 * one comparison.  Many places in the kernel can bypass this full check

 * if they have already ruled out V8086 mode, so user_mode(regs) can be used.

 */

static inline int user_mode(struct pt_regs *regs)

{

	return (regs->xcs & 3) != 0;