From 1379a5ce3ffc549a7ff3daffc49c5e1c372717a3 Mon Sep 17 00:00:00 2001 From: Harvey Harrison Date: Wed, 30 Jan 2008 13:33:00 +0100 Subject: x86: move get_segment_eip() to step.c get_segment_eip has similarities to convert_rip_to_linear(), and is used in a similar context. Move get_segment_eip to step.c to allow easier consolidation. Signed-off-by: Harvey Harrison Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner --- arch/x86/kernel/step.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+) (limited to 'arch/x86/kernel/step.c') diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c index 21ea22f..5884dd4 100644 --- a/arch/x86/kernel/step.c +++ b/arch/x86/kernel/step.c @@ -6,6 +6,87 @@ #include #ifdef CONFIG_X86_32 +#include + +#include + +/* + * Return EIP plus the CS segment base. The segment limit is also + * adjusted, clamped to the kernel/user address space (whichever is + * appropriate), and returned in *eip_limit. + * + * The segment is checked, because it might have been changed by another + * task between the original faulting instruction and here. + * + * If CS is no longer a valid code segment, or if EIP is beyond the + * limit, or if it is a kernel address when CS is not a kernel segment, + * then the returned value will be greater than *eip_limit. + * + * This is slow, but is very rarely executed. + */ +unsigned long get_segment_eip(struct pt_regs *regs, + unsigned long *eip_limit) +{ + unsigned long ip = regs->ip; + unsigned seg = regs->cs & 0xffff; + u32 seg_ar, seg_limit, base, *desc; + + /* Unlikely, but must come before segment checks. */ + if (unlikely(regs->flags & VM_MASK)) { + base = seg << 4; + *eip_limit = base + 0xffff; + return base + (ip & 0xffff); + } + + /* The standard kernel/user address space limit. */ + *eip_limit = user_mode(regs) ? USER_DS.seg : KERNEL_DS.seg; + + /* By far the most common cases. */ + if (likely(SEGMENT_IS_FLAT_CODE(seg))) + return ip; + + /* Check the segment exists, is within the current LDT/GDT size, + that kernel/user (ring 0..3) has the appropriate privilege, + that it's a code segment, and get the limit. */ + __asm__("larl %3,%0; lsll %3,%1" + : "=&r" (seg_ar), "=r" (seg_limit) : "0" (0), "rm" (seg)); + if ((~seg_ar & 0x9800) || ip > seg_limit) { + *eip_limit = 0; + return 1; /* So that returned ip > *eip_limit. */ + } + + /* Get the GDT/LDT descriptor base. + When you look for races in this code remember that + LDT and other horrors are only used in user space. */ + if (seg & (1<<2)) { + /* Must lock the LDT while reading it. */ + mutex_lock(¤t->mm->context.lock); + desc = current->mm->context.ldt; + desc = (void *)desc + (seg & ~7); + } else { + /* Must disable preemption while reading the GDT. */ + desc = (u32 *)get_cpu_gdt_table(get_cpu()); + desc = (void *)desc + (seg & ~7); + } + + /* Decode the code segment base from the descriptor */ + base = get_desc_base((struct desc_struct *)desc); + + if (seg & (1<<2)) + mutex_unlock(¤t->mm->context.lock); + else + put_cpu(); + + /* Adjust EIP and segment limit, and clamp at the kernel limit. + It's legitimate for segments to wrap at 0xffffffff. */ + seg_limit += base; + if (seg_limit < *eip_limit && seg_limit >= base) + *eip_limit = seg_limit; + return ip + base; +} +#endif + +#ifdef CONFIG_X86_32 static #endif unsigned long convert_rip_to_linear(struct task_struct *child, struct pt_regs *regs) -- cgit v1.1