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Diffstat (limited to 'arch/x86/kernel/doublefault_32.c')
| -rw-r--r-- | arch/x86/kernel/doublefault_32.c | 133 |
1 files changed, 133 insertions, 0 deletions
diff --git a/arch/x86/kernel/doublefault_32.c b/arch/x86/kernel/doublefault_32.c new file mode 100644 index 000000000..759d392cb --- /dev/null +++ b/arch/x86/kernel/doublefault_32.c @@ -0,0 +1,133 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/mm.h> +#include <linux/sched.h> +#include <linux/sched/debug.h> +#include <linux/init_task.h> +#include <linux/fs.h> + +#include <linux/uaccess.h> +#include <asm/processor.h> +#include <asm/desc.h> +#include <asm/traps.h> + +#define ptr_ok(x) ((x) > PAGE_OFFSET && (x) < PAGE_OFFSET + MAXMEM) + +#define TSS(x) this_cpu_read(cpu_tss_rw.x86_tss.x) + +static void set_df_gdt_entry(unsigned int cpu); + +/* + * Called by double_fault with CR0.TS and EFLAGS.NT cleared. The CPU thinks + * we're running the doublefault task. Cannot return. + */ +asmlinkage noinstr void __noreturn doublefault_shim(void) +{ + unsigned long cr2; + struct pt_regs regs; + + BUILD_BUG_ON(sizeof(struct doublefault_stack) != PAGE_SIZE); + + cr2 = native_read_cr2(); + + /* Reset back to the normal kernel task. */ + force_reload_TR(); + set_df_gdt_entry(smp_processor_id()); + + trace_hardirqs_off(); + + /* + * Fill in pt_regs. A downside of doing this in C is that the unwinder + * won't see it (no ENCODE_FRAME_POINTER), so a nested stack dump + * won't successfully unwind to the source of the double fault. + * The main dump from exc_double_fault() is fine, though, since it + * uses these regs directly. + * + * If anyone ever cares, this could be moved to asm. + */ + regs.ss = TSS(ss); + regs.__ssh = 0; + regs.sp = TSS(sp); + regs.flags = TSS(flags); + regs.cs = TSS(cs); + /* We won't go through the entry asm, so we can leave __csh as 0. */ + regs.__csh = 0; + regs.ip = TSS(ip); + regs.orig_ax = 0; + regs.gs = TSS(gs); + regs.__gsh = 0; + regs.fs = TSS(fs); + regs.__fsh = 0; + regs.es = TSS(es); + regs.__esh = 0; + regs.ds = TSS(ds); + regs.__dsh = 0; + regs.ax = TSS(ax); + regs.bp = TSS(bp); + regs.di = TSS(di); + regs.si = TSS(si); + regs.dx = TSS(dx); + regs.cx = TSS(cx); + regs.bx = TSS(bx); + + exc_double_fault(®s, 0, cr2); + + /* + * x86_32 does not save the original CR3 anywhere on a task switch. + * This means that, even if we wanted to return, we would need to find + * some way to reconstruct CR3. We could make a credible guess based + * on cpu_tlbstate, but that would be racy and would not account for + * PTI. + * + * Instead, don't bother. We can return through + * rewind_stack_do_exit() instead. + */ + panic("cannot return from double fault\n"); +} + +DEFINE_PER_CPU_PAGE_ALIGNED(struct doublefault_stack, doublefault_stack) = { + .tss = { + /* + * No sp0 or ss0 -- we never run CPL != 0 with this TSS + * active. sp is filled in later. + */ + .ldt = 0, + .io_bitmap_base = IO_BITMAP_OFFSET_INVALID, + + .ip = (unsigned long) asm_exc_double_fault, + .flags = X86_EFLAGS_FIXED, + .es = __USER_DS, + .cs = __KERNEL_CS, + .ss = __KERNEL_DS, + .ds = __USER_DS, + .fs = __KERNEL_PERCPU, +#ifndef CONFIG_X86_32_LAZY_GS + .gs = __KERNEL_STACK_CANARY, +#endif + + .__cr3 = __pa_nodebug(swapper_pg_dir), + }, +}; + +static void set_df_gdt_entry(unsigned int cpu) +{ + /* Set up doublefault TSS pointer in the GDT */ + __set_tss_desc(cpu, GDT_ENTRY_DOUBLEFAULT_TSS, + &get_cpu_entry_area(cpu)->doublefault_stack.tss); + +} + +void doublefault_init_cpu_tss(void) +{ + unsigned int cpu = smp_processor_id(); + struct cpu_entry_area *cea = get_cpu_entry_area(cpu); + + /* + * The linker isn't smart enough to initialize percpu variables that + * point to other places in percpu space. + */ + this_cpu_write(doublefault_stack.tss.sp, + (unsigned long)&cea->doublefault_stack.stack + + sizeof(doublefault_stack.stack)); + + set_df_gdt_entry(cpu); +} |