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f7bafa2b05
Same as is done for syscalls, interleave XOR with PUSH instructions for exceptions/interrupts, in order to minimize the cost of the additional instructions required for register clearing. Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: dan.j.williams@intel.com Link: http://lkml.kernel.org/r/20180211104949.12992-4-linux@dominikbrodowski.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
349 lines
9.6 KiB
C
349 lines
9.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#include <linux/jump_label.h>
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#include <asm/unwind_hints.h>
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#include <asm/cpufeatures.h>
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#include <asm/page_types.h>
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#include <asm/percpu.h>
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#include <asm/asm-offsets.h>
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#include <asm/processor-flags.h>
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/*
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x86 function call convention, 64-bit:
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-------------------------------------
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arguments | callee-saved | extra caller-saved | return
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[callee-clobbered] | | [callee-clobbered] |
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---------------------------------------------------------------------------
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rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**]
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( rsp is obviously invariant across normal function calls. (gcc can 'merge'
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functions when it sees tail-call optimization possibilities) rflags is
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clobbered. Leftover arguments are passed over the stack frame.)
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[*] In the frame-pointers case rbp is fixed to the stack frame.
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[**] for struct return values wider than 64 bits the return convention is a
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bit more complex: up to 128 bits width we return small structures
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straight in rax, rdx. For structures larger than that (3 words or
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larger) the caller puts a pointer to an on-stack return struct
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[allocated in the caller's stack frame] into the first argument - i.e.
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into rdi. All other arguments shift up by one in this case.
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Fortunately this case is rare in the kernel.
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For 32-bit we have the following conventions - kernel is built with
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-mregparm=3 and -freg-struct-return:
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x86 function calling convention, 32-bit:
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----------------------------------------
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arguments | callee-saved | extra caller-saved | return
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[callee-clobbered] | | [callee-clobbered] |
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-------------------------------------------------------------------------
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eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**]
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( here too esp is obviously invariant across normal function calls. eflags
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is clobbered. Leftover arguments are passed over the stack frame. )
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[*] In the frame-pointers case ebp is fixed to the stack frame.
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[**] We build with -freg-struct-return, which on 32-bit means similar
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semantics as on 64-bit: edx can be used for a second return value
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(i.e. covering integer and structure sizes up to 64 bits) - after that
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it gets more complex and more expensive: 3-word or larger struct returns
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get done in the caller's frame and the pointer to the return struct goes
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into regparm0, i.e. eax - the other arguments shift up and the
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function's register parameters degenerate to regparm=2 in essence.
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*/
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#ifdef CONFIG_X86_64
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/*
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* 64-bit system call stack frame layout defines and helpers,
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* for assembly code:
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*/
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/* The layout forms the "struct pt_regs" on the stack: */
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/*
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* C ABI says these regs are callee-preserved. They aren't saved on kernel entry
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* unless syscall needs a complete, fully filled "struct pt_regs".
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*/
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#define R15 0*8
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#define R14 1*8
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#define R13 2*8
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#define R12 3*8
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#define RBP 4*8
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#define RBX 5*8
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/* These regs are callee-clobbered. Always saved on kernel entry. */
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#define R11 6*8
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#define R10 7*8
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#define R9 8*8
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#define R8 9*8
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#define RAX 10*8
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#define RCX 11*8
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#define RDX 12*8
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#define RSI 13*8
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#define RDI 14*8
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/*
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* On syscall entry, this is syscall#. On CPU exception, this is error code.
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* On hw interrupt, it's IRQ number:
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*/
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#define ORIG_RAX 15*8
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/* Return frame for iretq */
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#define RIP 16*8
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#define CS 17*8
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#define EFLAGS 18*8
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#define RSP 19*8
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#define SS 20*8
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#define SIZEOF_PTREGS 21*8
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.macro ALLOC_PT_GPREGS_ON_STACK
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addq $-(15*8), %rsp
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.endm
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.macro SAVE_AND_CLEAR_REGS offset=0
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/*
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* Save registers and sanitize registers of values that a
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* speculation attack might otherwise want to exploit. The
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* lower registers are likely clobbered well before they
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* could be put to use in a speculative execution gadget.
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* Interleave XOR with PUSH for better uop scheduling:
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*/
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movq %rdi, 14*8+\offset(%rsp)
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movq %rsi, 13*8+\offset(%rsp)
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movq %rdx, 12*8+\offset(%rsp)
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movq %rcx, 11*8+\offset(%rsp)
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movq %rax, 10*8+\offset(%rsp)
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movq %r8, 9*8+\offset(%rsp)
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xorq %r8, %r8 /* nospec r8 */
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movq %r9, 8*8+\offset(%rsp)
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xorq %r9, %r9 /* nospec r9 */
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movq %r10, 7*8+\offset(%rsp)
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xorq %r10, %r10 /* nospec r10 */
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movq %r11, 6*8+\offset(%rsp)
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xorq %r11, %r11 /* nospec r11 */
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movq %rbx, 5*8+\offset(%rsp)
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xorl %ebx, %ebx /* nospec rbx */
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movq %rbp, 4*8+\offset(%rsp)
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xorl %ebp, %ebp /* nospec rbp */
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movq %r12, 3*8+\offset(%rsp)
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xorq %r12, %r12 /* nospec r12 */
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movq %r13, 2*8+\offset(%rsp)
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xorq %r13, %r13 /* nospec r13 */
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movq %r14, 1*8+\offset(%rsp)
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xorq %r14, %r14 /* nospec r14 */
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movq %r15, 0*8+\offset(%rsp)
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xorq %r15, %r15 /* nospec r15 */
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UNWIND_HINT_REGS offset=\offset
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.endm
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.macro POP_REGS pop_rdi=1 skip_r11rcx=0
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popq %r15
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popq %r14
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popq %r13
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popq %r12
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popq %rbp
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popq %rbx
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.if \skip_r11rcx
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popq %rsi
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.else
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popq %r11
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.endif
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popq %r10
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popq %r9
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popq %r8
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popq %rax
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.if \skip_r11rcx
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popq %rsi
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.else
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popq %rcx
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.endif
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popq %rdx
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popq %rsi
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.if \pop_rdi
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popq %rdi
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.endif
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.endm
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.macro icebp
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.byte 0xf1
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.endm
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/*
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* This is a sneaky trick to help the unwinder find pt_regs on the stack. The
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* frame pointer is replaced with an encoded pointer to pt_regs. The encoding
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* is just setting the LSB, which makes it an invalid stack address and is also
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* a signal to the unwinder that it's a pt_regs pointer in disguise.
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*
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* NOTE: This macro must be used *after* SAVE_AND_CLEAR_REGS because it corrupts
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* the original rbp.
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*/
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.macro ENCODE_FRAME_POINTER ptregs_offset=0
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#ifdef CONFIG_FRAME_POINTER
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.if \ptregs_offset
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leaq \ptregs_offset(%rsp), %rbp
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.else
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mov %rsp, %rbp
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.endif
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orq $0x1, %rbp
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#endif
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.endm
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#ifdef CONFIG_PAGE_TABLE_ISOLATION
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/*
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* PAGE_TABLE_ISOLATION PGDs are 8k. Flip bit 12 to switch between the two
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* halves:
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*/
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#define PTI_USER_PGTABLE_BIT PAGE_SHIFT
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#define PTI_USER_PGTABLE_MASK (1 << PTI_USER_PGTABLE_BIT)
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#define PTI_USER_PCID_BIT X86_CR3_PTI_PCID_USER_BIT
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#define PTI_USER_PCID_MASK (1 << PTI_USER_PCID_BIT)
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#define PTI_USER_PGTABLE_AND_PCID_MASK (PTI_USER_PCID_MASK | PTI_USER_PGTABLE_MASK)
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.macro SET_NOFLUSH_BIT reg:req
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bts $X86_CR3_PCID_NOFLUSH_BIT, \reg
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.endm
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.macro ADJUST_KERNEL_CR3 reg:req
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ALTERNATIVE "", "SET_NOFLUSH_BIT \reg", X86_FEATURE_PCID
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/* Clear PCID and "PAGE_TABLE_ISOLATION bit", point CR3 at kernel pagetables: */
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andq $(~PTI_USER_PGTABLE_AND_PCID_MASK), \reg
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.endm
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.macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
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ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
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mov %cr3, \scratch_reg
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ADJUST_KERNEL_CR3 \scratch_reg
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mov \scratch_reg, %cr3
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.Lend_\@:
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.endm
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#define THIS_CPU_user_pcid_flush_mask \
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PER_CPU_VAR(cpu_tlbstate) + TLB_STATE_user_pcid_flush_mask
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.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req
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ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
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mov %cr3, \scratch_reg
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ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID
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/*
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* Test if the ASID needs a flush.
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*/
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movq \scratch_reg, \scratch_reg2
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andq $(0x7FF), \scratch_reg /* mask ASID */
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bt \scratch_reg, THIS_CPU_user_pcid_flush_mask
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jnc .Lnoflush_\@
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/* Flush needed, clear the bit */
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btr \scratch_reg, THIS_CPU_user_pcid_flush_mask
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movq \scratch_reg2, \scratch_reg
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jmp .Lwrcr3_pcid_\@
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.Lnoflush_\@:
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movq \scratch_reg2, \scratch_reg
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SET_NOFLUSH_BIT \scratch_reg
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.Lwrcr3_pcid_\@:
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/* Flip the ASID to the user version */
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orq $(PTI_USER_PCID_MASK), \scratch_reg
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.Lwrcr3_\@:
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/* Flip the PGD to the user version */
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orq $(PTI_USER_PGTABLE_MASK), \scratch_reg
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mov \scratch_reg, %cr3
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.Lend_\@:
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.endm
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.macro SWITCH_TO_USER_CR3_STACK scratch_reg:req
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pushq %rax
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SWITCH_TO_USER_CR3_NOSTACK scratch_reg=\scratch_reg scratch_reg2=%rax
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popq %rax
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.endm
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.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
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ALTERNATIVE "jmp .Ldone_\@", "", X86_FEATURE_PTI
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movq %cr3, \scratch_reg
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movq \scratch_reg, \save_reg
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/*
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* Test the user pagetable bit. If set, then the user page tables
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* are active. If clear CR3 already has the kernel page table
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* active.
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*/
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bt $PTI_USER_PGTABLE_BIT, \scratch_reg
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jnc .Ldone_\@
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ADJUST_KERNEL_CR3 \scratch_reg
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movq \scratch_reg, %cr3
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.Ldone_\@:
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.endm
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.macro RESTORE_CR3 scratch_reg:req save_reg:req
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ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
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ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID
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/*
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* KERNEL pages can always resume with NOFLUSH as we do
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* explicit flushes.
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*/
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bt $PTI_USER_PGTABLE_BIT, \save_reg
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jnc .Lnoflush_\@
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/*
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* Check if there's a pending flush for the user ASID we're
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* about to set.
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*/
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movq \save_reg, \scratch_reg
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andq $(0x7FF), \scratch_reg
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bt \scratch_reg, THIS_CPU_user_pcid_flush_mask
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jnc .Lnoflush_\@
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btr \scratch_reg, THIS_CPU_user_pcid_flush_mask
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jmp .Lwrcr3_\@
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.Lnoflush_\@:
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SET_NOFLUSH_BIT \save_reg
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.Lwrcr3_\@:
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/*
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* The CR3 write could be avoided when not changing its value,
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* but would require a CR3 read *and* a scratch register.
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*/
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movq \save_reg, %cr3
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.Lend_\@:
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.endm
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#else /* CONFIG_PAGE_TABLE_ISOLATION=n: */
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.macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
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.endm
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.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req
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.endm
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.macro SWITCH_TO_USER_CR3_STACK scratch_reg:req
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.endm
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.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
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.endm
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.macro RESTORE_CR3 scratch_reg:req save_reg:req
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.endm
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#endif
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#endif /* CONFIG_X86_64 */
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/*
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* This does 'call enter_from_user_mode' unless we can avoid it based on
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* kernel config or using the static jump infrastructure.
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*/
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.macro CALL_enter_from_user_mode
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#ifdef CONFIG_CONTEXT_TRACKING
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#ifdef HAVE_JUMP_LABEL
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STATIC_JUMP_IF_FALSE .Lafter_call_\@, context_tracking_enabled, def=0
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#endif
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call enter_from_user_mode
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.Lafter_call_\@:
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#endif
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.endm
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