Messages in this thread Patch in this message | | | Date | Wed, 3 Aug 2005 17:43:24 -0700 | From | zach@vmware ... | Subject | [PATCH] 2/5 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> Index: linux-2.6.13/arch/i386/kernel/signal.c =================================================================== --- linux-2.6.13.orig/arch/i386/kernel/signal.c 2005-08-02 17:06:21.000000000 -0700 +++ linux-2.6.13/arch/i386/kernel/signal.c 2005-08-02 17:09:54.000000000 -0700 @@ -603,7 +603,9 @@ * 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; Index: linux-2.6.13/arch/i386/kernel/traps.c =================================================================== --- linux-2.6.13.orig/arch/i386/kernel/traps.c 2005-08-02 17:06:21.000000000 -0700 +++ linux-2.6.13/arch/i386/kernel/traps.c 2005-08-02 17:09:54.000000000 -0700 @@ -245,7 +245,7 @@ unsigned short ss; esp = (unsigned long) (®s->esp); - ss = __KERNEL_DS; + savesegment(ss, ss); if (user_mode(regs)) { in_kernel = 0; esp = regs->esp; @@ -302,9 +302,6 @@ char c; unsigned long eip; - if (user_mode(regs)) - goto no_bug; /* Not in kernel */ - eip = regs->eip; if (eip < PAGE_OFFSET) Index: linux-2.6.13/include/asm-i386/ptrace.h =================================================================== --- linux-2.6.13.orig/include/asm-i386/ptrace.h 2005-08-02 17:04:23.000000000 -0700 +++ linux-2.6.13/include/asm-i386/ptrace.h 2005-08-02 17:09:54.000000000 -0700 @@ -61,6 +61,13 @@ 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; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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