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6ab80d88f8
I do not see panic calling rewind_stack_do_exit anywhere, nor can I
find anywhere in the history where doublefault_shim has called
rewind_stack_do_exit. So I don't think this comment was ever actually
correct.
Cc: Andy Lutomirski <luto@kernel.org>
Fixes: 7d8d8cfdee ("x86/doublefault/32: Rewrite the x86_32 #DF handler and unify with 64-bit")
Link: https://lkml.kernel.org/r/20211020174406.17889-1-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
128 lines
3.3 KiB
C
128 lines
3.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/mm.h>
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#include <linux/sched.h>
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#include <linux/sched/debug.h>
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#include <linux/init_task.h>
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#include <linux/fs.h>
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#include <linux/uaccess.h>
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#include <asm/processor.h>
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#include <asm/desc.h>
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#include <asm/traps.h>
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#define ptr_ok(x) ((x) > PAGE_OFFSET && (x) < PAGE_OFFSET + MAXMEM)
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#define TSS(x) this_cpu_read(cpu_tss_rw.x86_tss.x)
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static void set_df_gdt_entry(unsigned int cpu);
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/*
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* Called by double_fault with CR0.TS and EFLAGS.NT cleared. The CPU thinks
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* we're running the doublefault task. Cannot return.
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*/
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asmlinkage noinstr void __noreturn doublefault_shim(void)
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{
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unsigned long cr2;
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struct pt_regs regs;
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BUILD_BUG_ON(sizeof(struct doublefault_stack) != PAGE_SIZE);
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cr2 = native_read_cr2();
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/* Reset back to the normal kernel task. */
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force_reload_TR();
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set_df_gdt_entry(smp_processor_id());
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trace_hardirqs_off();
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/*
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* Fill in pt_regs. A downside of doing this in C is that the unwinder
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* won't see it (no ENCODE_FRAME_POINTER), so a nested stack dump
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* won't successfully unwind to the source of the double fault.
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* The main dump from exc_double_fault() is fine, though, since it
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* uses these regs directly.
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*
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* If anyone ever cares, this could be moved to asm.
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*/
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regs.ss = TSS(ss);
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regs.__ssh = 0;
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regs.sp = TSS(sp);
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regs.flags = TSS(flags);
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regs.cs = TSS(cs);
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/* We won't go through the entry asm, so we can leave __csh as 0. */
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regs.__csh = 0;
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regs.ip = TSS(ip);
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regs.orig_ax = 0;
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regs.gs = TSS(gs);
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regs.__gsh = 0;
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regs.fs = TSS(fs);
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regs.__fsh = 0;
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regs.es = TSS(es);
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regs.__esh = 0;
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regs.ds = TSS(ds);
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regs.__dsh = 0;
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regs.ax = TSS(ax);
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regs.bp = TSS(bp);
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regs.di = TSS(di);
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regs.si = TSS(si);
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regs.dx = TSS(dx);
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regs.cx = TSS(cx);
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regs.bx = TSS(bx);
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exc_double_fault(®s, 0, cr2);
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/*
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* x86_32 does not save the original CR3 anywhere on a task switch.
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* This means that, even if we wanted to return, we would need to find
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* some way to reconstruct CR3. We could make a credible guess based
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* on cpu_tlbstate, but that would be racy and would not account for
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* PTI.
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*/
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panic("cannot return from double fault\n");
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}
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DEFINE_PER_CPU_PAGE_ALIGNED(struct doublefault_stack, doublefault_stack) = {
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.tss = {
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/*
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* No sp0 or ss0 -- we never run CPL != 0 with this TSS
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* active. sp is filled in later.
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*/
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.ldt = 0,
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.io_bitmap_base = IO_BITMAP_OFFSET_INVALID,
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.ip = (unsigned long) asm_exc_double_fault,
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.flags = X86_EFLAGS_FIXED,
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.es = __USER_DS,
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.cs = __KERNEL_CS,
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.ss = __KERNEL_DS,
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.ds = __USER_DS,
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.fs = __KERNEL_PERCPU,
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.gs = 0,
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.__cr3 = __pa_nodebug(swapper_pg_dir),
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},
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};
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static void set_df_gdt_entry(unsigned int cpu)
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{
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/* Set up doublefault TSS pointer in the GDT */
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__set_tss_desc(cpu, GDT_ENTRY_DOUBLEFAULT_TSS,
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&get_cpu_entry_area(cpu)->doublefault_stack.tss);
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}
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void doublefault_init_cpu_tss(void)
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{
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unsigned int cpu = smp_processor_id();
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struct cpu_entry_area *cea = get_cpu_entry_area(cpu);
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/*
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* The linker isn't smart enough to initialize percpu variables that
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* point to other places in percpu space.
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*/
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this_cpu_write(doublefault_stack.tss.sp,
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(unsigned long)&cea->doublefault_stack.stack +
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sizeof(doublefault_stack.stack));
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set_df_gdt_entry(cpu);
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}
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