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3fb0fdb3bb
On 32-bit kernels, the stackprotector canary is quite nasty -- it is stored at %gs:(20), which is nasty because 32-bit kernels use %fs for percpu storage. It's even nastier because it means that whether %gs contains userspace state or kernel state while running kernel code depends on whether stackprotector is enabled (this is CONFIG_X86_32_LAZY_GS), and this setting radically changes the way that segment selectors work. Supporting both variants is a maintenance and testing mess. Merely rearranging so that percpu and the stack canary share the same segment would be messy as the 32-bit percpu address layout isn't currently compatible with putting a variable at a fixed offset. Fortunately, GCC 8.1 added options that allow the stack canary to be accessed as %fs:__stack_chk_guard, effectively turning it into an ordinary percpu variable. This lets us get rid of all of the code to manage the stack canary GDT descriptor and the CONFIG_X86_32_LAZY_GS mess. (That name is special. We could use any symbol we want for the %fs-relative mode, but for CONFIG_SMP=n, gcc refuses to let us use any name other than __stack_chk_guard.) Forcibly disable stackprotector on older compilers that don't support the new options and turn the stack canary into a percpu variable. The "lazy GS" approach is now used for all 32-bit configurations. Also makes load_gs_index() work on 32-bit kernels. On 64-bit kernels, it loads the GS selector and updates the user GSBASE accordingly. (This is unchanged.) On 32-bit kernels, it loads the GS selector and updates GSBASE, which is now always the user base. This means that the overall effect is the same on 32-bit and 64-bit, which avoids some ifdeffery. [ bp: Massage commit message. ] Signed-off-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Borislav Petkov <bp@suse.de> Link: https://lkml.kernel.org/r/c0ff7dba14041c7e5d1cae5d4df052f03759bef3.1613243844.git.luto@kernel.org
37 lines
876 B
C
37 lines
876 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright 2001-2002 Pavel Machek <pavel@suse.cz>
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* Based on code
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* Copyright 2001 Patrick Mochel <mochel@osdl.org>
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*/
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#ifndef _ASM_X86_SUSPEND_32_H
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#define _ASM_X86_SUSPEND_32_H
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#include <asm/desc.h>
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#include <asm/fpu/api.h>
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/* image of the saved processor state */
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struct saved_context {
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/*
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* On x86_32, all segment registers except gs are saved at kernel
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* entry in pt_regs.
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*/
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u16 gs;
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unsigned long cr0, cr2, cr3, cr4;
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u64 misc_enable;
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bool misc_enable_saved;
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struct saved_msrs saved_msrs;
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struct desc_ptr gdt_desc;
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struct desc_ptr idt;
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u16 ldt;
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u16 tss;
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unsigned long tr;
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unsigned long safety;
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unsigned long return_address;
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} __attribute__((packed));
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/* routines for saving/restoring kernel state */
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extern char core_restore_code[];
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extern char restore_registers[];
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#endif /* _ASM_X86_SUSPEND_32_H */
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