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x86/entry: Add kernel IBRS implementation
Implement Kernel IBRS - currently the only known option to mitigate RSB underflow speculation issues on Skylake hardware. Note: since IBRS_ENTER requires fuller context established than UNTRAIN_RET, it must be placed after it. However, since UNTRAIN_RET itself implies a RET, it must come after IBRS_ENTER. This means IBRS_ENTER needs to also move UNTRAIN_RET. Note 2: KERNEL_IBRS is sub-optimal for XenPV. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Borislav Petkov <bp@suse.de>
This commit is contained in:
Peter Zijlstra
Borislav Petkov
parent
caa0ff24d5
commit
2dbb887e87
4 changed files with 111 additions and 10 deletions
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@ -7,6 +7,8 @@
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#include <asm/asm-offsets.h>
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#include <asm/processor-flags.h>
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#include <asm/ptrace-abi.h>
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#include <asm/msr.h>
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#include <asm/nospec-branch.h>
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/*
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@ -282,6 +284,62 @@ For 32-bit we have the following conventions - kernel is built with
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#endif
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/*
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* IBRS kernel mitigation for Spectre_v2.
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*
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* Assumes full context is established (PUSH_REGS, CR3 and GS) and it clobbers
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* the regs it uses (AX, CX, DX). Must be called before the first RET
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* instruction (NOTE! UNTRAIN_RET includes a RET instruction)
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*
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* The optional argument is used to save/restore the current value,
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* which is used on the paranoid paths.
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*
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* Assumes x86_spec_ctrl_{base,current} to have SPEC_CTRL_IBRS set.
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*/
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.macro IBRS_ENTER save_reg
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ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
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movl $MSR_IA32_SPEC_CTRL, %ecx
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.ifnb \save_reg
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rdmsr
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shl $32, %rdx
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or %rdx, %rax
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mov %rax, \save_reg
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test $SPEC_CTRL_IBRS, %eax
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jz .Ldo_wrmsr_\@
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lfence
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jmp .Lend_\@
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.Ldo_wrmsr_\@:
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.endif
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movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx
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movl %edx, %eax
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shr $32, %rdx
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wrmsr
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.Lend_\@:
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.endm
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/*
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* Similar to IBRS_ENTER, requires KERNEL GS,CR3 and clobbers (AX, CX, DX)
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* regs. Must be called after the last RET.
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*/
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.macro IBRS_EXIT save_reg
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ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
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movl $MSR_IA32_SPEC_CTRL, %ecx
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.ifnb \save_reg
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mov \save_reg, %rdx
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.else
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movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx
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andl $(~SPEC_CTRL_IBRS), %edx
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.endif
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movl %edx, %eax
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shr $32, %rdx
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wrmsr
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.Lend_\@:
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.endm
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/*
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* Mitigate Spectre v1 for conditional swapgs code paths.
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*
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@ -96,7 +96,6 @@ SYM_CODE_START(entry_SYSCALL_64)
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SYM_INNER_LABEL(entry_SYSCALL_64_safe_stack, SYM_L_GLOBAL)
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ANNOTATE_NOENDBR
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UNTRAIN_RET
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/* Construct struct pt_regs on stack */
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pushq $__USER_DS /* pt_regs->ss */
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@ -113,6 +112,11 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
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movq %rsp, %rdi
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/* Sign extend the lower 32bit as syscall numbers are treated as int */
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movslq %eax, %rsi
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/* clobbers %rax, make sure it is after saving the syscall nr */
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IBRS_ENTER
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UNTRAIN_RET
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call do_syscall_64 /* returns with IRQs disabled */
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/*
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@ -192,6 +196,7 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
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* perf profiles. Nothing jumps here.
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*/
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syscall_return_via_sysret:
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IBRS_EXIT
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POP_REGS pop_rdi=0
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/*
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@ -605,6 +610,7 @@ __irqentry_text_end:
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SYM_CODE_START_LOCAL(common_interrupt_return)
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SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
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IBRS_EXIT
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#ifdef CONFIG_DEBUG_ENTRY
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/* Assert that pt_regs indicates user mode. */
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testb $3, CS(%rsp)
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@ -891,6 +897,9 @@ SYM_CODE_END(xen_failsafe_callback)
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* 1 -> no SWAPGS on exit
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*
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* Y GSBASE value at entry, must be restored in paranoid_exit
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*
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* R14 - old CR3
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* R15 - old SPEC_CTRL
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*/
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SYM_CODE_START_LOCAL(paranoid_entry)
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UNWIND_HINT_FUNC
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@ -913,7 +922,6 @@ SYM_CODE_START_LOCAL(paranoid_entry)
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* be retrieved from a kernel internal table.
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*/
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SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14
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UNTRAIN_RET
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/*
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* Handling GSBASE depends on the availability of FSGSBASE.
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@ -935,7 +943,7 @@ SYM_CODE_START_LOCAL(paranoid_entry)
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* is needed here.
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*/
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SAVE_AND_SET_GSBASE scratch_reg=%rax save_reg=%rbx
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RET
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jmp .Lparanoid_gsbase_done
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.Lparanoid_entry_checkgs:
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/* EBX = 1 -> kernel GSBASE active, no restore required */
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@ -954,8 +962,16 @@ SYM_CODE_START_LOCAL(paranoid_entry)
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xorl %ebx, %ebx
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swapgs
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.Lparanoid_kernel_gsbase:
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FENCE_SWAPGS_KERNEL_ENTRY
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.Lparanoid_gsbase_done:
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/*
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* Once we have CR3 and %GS setup save and set SPEC_CTRL. Just like
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* CR3 above, keep the old value in a callee saved register.
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*/
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IBRS_ENTER save_reg=%r15
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UNTRAIN_RET
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RET
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SYM_CODE_END(paranoid_entry)
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@ -977,9 +993,19 @@ SYM_CODE_END(paranoid_entry)
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* 1 -> no SWAPGS on exit
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*
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* Y User space GSBASE, must be restored unconditionally
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*
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* R14 - old CR3
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* R15 - old SPEC_CTRL
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*/
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SYM_CODE_START_LOCAL(paranoid_exit)
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UNWIND_HINT_REGS
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/*
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* Must restore IBRS state before both CR3 and %GS since we need access
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* to the per-CPU x86_spec_ctrl_shadow variable.
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*/
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IBRS_EXIT save_reg=%r15
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/*
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* The order of operations is important. RESTORE_CR3 requires
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* kernel GSBASE.
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@ -1023,10 +1049,12 @@ SYM_CODE_START_LOCAL(error_entry)
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FENCE_SWAPGS_USER_ENTRY
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/* We have user CR3. Change to kernel CR3. */
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SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
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IBRS_ENTER
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UNTRAIN_RET
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leaq 8(%rsp), %rdi /* arg0 = pt_regs pointer */
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.Lerror_entry_from_usermode_after_swapgs:
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/* Put us onto the real thread stack. */
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call sync_regs
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RET
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@ -1076,6 +1104,7 @@ SYM_CODE_START_LOCAL(error_entry)
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swapgs
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FENCE_SWAPGS_USER_ENTRY
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SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
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IBRS_ENTER
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UNTRAIN_RET
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/*
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@ -1172,7 +1201,6 @@ SYM_CODE_START(asm_exc_nmi)
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movq %rsp, %rdx
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movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
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UNWIND_HINT_IRET_REGS base=%rdx offset=8
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UNTRAIN_RET
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pushq 5*8(%rdx) /* pt_regs->ss */
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pushq 4*8(%rdx) /* pt_regs->rsp */
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pushq 3*8(%rdx) /* pt_regs->flags */
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@ -1183,6 +1211,9 @@ SYM_CODE_START(asm_exc_nmi)
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PUSH_AND_CLEAR_REGS rdx=(%rdx)
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ENCODE_FRAME_POINTER
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IBRS_ENTER
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UNTRAIN_RET
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/*
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* At this point we no longer need to worry about stack damage
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* due to nesting -- we're on the normal thread stack and we're
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@ -1407,6 +1438,9 @@ end_repeat_nmi:
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movq $-1, %rsi
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call exc_nmi
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/* Always restore stashed SPEC_CTRL value (see paranoid_entry) */
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IBRS_EXIT save_reg=%r15
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/* Always restore stashed CR3 value (see paranoid_entry) */
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RESTORE_CR3 scratch_reg=%r15 save_reg=%r14
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@ -4,7 +4,6 @@
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*
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* Copyright 2000-2002 Andi Kleen, SuSE Labs.
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*/
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#include "calling.h"
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#include <asm/asm-offsets.h>
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#include <asm/current.h>
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#include <asm/errno.h>
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@ -18,6 +17,8 @@
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#include <linux/linkage.h>
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#include <linux/err.h>
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#include "calling.h"
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.section .entry.text, "ax"
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/*
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@ -73,7 +74,6 @@ SYM_CODE_START(entry_SYSENTER_compat)
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pushq $__USER32_CS /* pt_regs->cs */
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pushq $0 /* pt_regs->ip = 0 (placeholder) */
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SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
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UNTRAIN_RET
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/*
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* User tracing code (ptrace or signal handlers) might assume that
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@ -90,6 +90,9 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
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cld
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IBRS_ENTER
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UNTRAIN_RET
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/*
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* SYSENTER doesn't filter flags, so we need to clear NT and AC
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* ourselves. To save a few cycles, we can check whether
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@ -192,7 +195,6 @@ SYM_CODE_START(entry_SYSCALL_compat)
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SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL)
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ANNOTATE_NOENDBR
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UNTRAIN_RET
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/* Construct struct pt_regs on stack */
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pushq $__USER32_DS /* pt_regs->ss */
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@ -206,6 +208,9 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
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PUSH_AND_CLEAR_REGS rcx=%rbp rax=$-ENOSYS
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UNWIND_HINT_REGS
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IBRS_ENTER
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UNTRAIN_RET
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movq %rsp, %rdi
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call do_fast_syscall_32
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/* XEN PV guests always use IRET path */
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@ -220,6 +225,8 @@ sysret32_from_system_call:
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*/
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STACKLEAK_ERASE
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IBRS_EXIT
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movq RBX(%rsp), %rbx /* pt_regs->rbx */
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movq RBP(%rsp), %rbp /* pt_regs->rbp */
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movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */
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@ -335,12 +342,14 @@ SYM_CODE_START(entry_INT80_compat)
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pushq 0*8(%rax) /* regs->orig_ax */
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.Lint80_keep_stack:
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UNTRAIN_RET
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PUSH_AND_CLEAR_REGS rax=$-ENOSYS
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UNWIND_HINT_REGS
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cld
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IBRS_ENTER
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UNTRAIN_RET
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movq %rsp, %rdi
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call do_int80_syscall_32
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jmp swapgs_restore_regs_and_return_to_usermode
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@ -203,7 +203,7 @@
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#define X86_FEATURE_PROC_FEEDBACK ( 7*32+ 9) /* AMD ProcFeedbackInterface */
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#define X86_FEATURE_XCOMPACTED ( 7*32+10) /* "" Use compacted XSTATE (XSAVES or XSAVEC) */
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#define X86_FEATURE_PTI ( 7*32+11) /* Kernel Page Table Isolation enabled */
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/* FREE! ( 7*32+12) */
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#define X86_FEATURE_KERNEL_IBRS ( 7*32+12) /* "" Set/clear IBRS on kernel entry/exit */
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/* FREE! ( 7*32+13) */
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#define X86_FEATURE_INTEL_PPIN ( 7*32+14) /* Intel Processor Inventory Number */
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#define X86_FEATURE_CDP_L2 ( 7*32+15) /* Code and Data Prioritization L2 */
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