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[PATCH] x86: privilege cleanup

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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: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Zachary Amsden 2005-09-03 15:56:43 -07:00 committed by Linus Torvalds
parent f2ab446124
commit 0998e4228a
3 changed files with 11 additions and 5 deletions
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4
arch/i386/kernel/signal.c
View File

@ -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;

5
arch/i386/kernel/traps.c
View File

@ -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)

7
include/asm-i386/ptrace.h
View File

@ -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;