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-rw-r--r--arch/x86/entry/entry_64.S96
1 files changed, 84 insertions, 12 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index bdb17fad5d..e986331b14 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -116,6 +116,7 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
/* clobbers %rax, make sure it is after saving the syscall nr */
IBRS_ENTER
UNTRAIN_RET
+ CLEAR_BRANCH_HISTORY
call do_syscall_64 /* returns with IRQs disabled */
@@ -560,17 +561,28 @@ __irqentry_text_end:
SYM_CODE_START_LOCAL(common_interrupt_return)
SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
IBRS_EXIT
-#ifdef CONFIG_DEBUG_ENTRY
- /* Assert that pt_regs indicates user mode. */
- testb $3, CS(%rsp)
- jnz 1f
- ud2
-1:
-#endif
#ifdef CONFIG_XEN_PV
ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
#endif
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+ ALTERNATIVE "", "jmp .Lpti_restore_regs_and_return_to_usermode", X86_FEATURE_PTI
+#endif
+ STACKLEAK_ERASE
+ POP_REGS
+ add $8, %rsp /* orig_ax */
+ UNWIND_HINT_IRET_REGS
+
+.Lswapgs_and_iret:
+ swapgs
+ CLEAR_CPU_BUFFERS
+ /* Assert that the IRET frame indicates user mode. */
+ testb $3, 8(%rsp)
+ jnz .Lnative_iret
+ ud2
+
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+.Lpti_restore_regs_and_return_to_usermode:
POP_REGS pop_rdi=0
/*
@@ -597,14 +609,14 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
*/
STACKLEAK_ERASE_NOCLOBBER
- SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
+ push %rax
+ SWITCH_TO_USER_CR3 scratch_reg=%rdi scratch_reg2=%rax
+ pop %rax
/* Restore RDI. */
popq %rdi
- swapgs
- CLEAR_CPU_BUFFERS
- jmp .Lnative_iret
-
+ jmp .Lswapgs_and_iret
+#endif
SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL)
#ifdef CONFIG_DEBUG_ENTRY
@@ -1483,3 +1495,63 @@ SYM_CODE_START_NOALIGN(rewind_stack_and_make_dead)
call make_task_dead
SYM_CODE_END(rewind_stack_and_make_dead)
.popsection
+
+/*
+ * This sequence executes branches in order to remove user branch information
+ * from the branch history tracker in the Branch Predictor, therefore removing
+ * user influence on subsequent BTB lookups.
+ *
+ * It should be used on parts prior to Alder Lake. Newer parts should use the
+ * BHI_DIS_S hardware control instead. If a pre-Alder Lake part is being
+ * virtualized on newer hardware the VMM should protect against BHI attacks by
+ * setting BHI_DIS_S for the guests.
+ *
+ * CALLs/RETs are necessary to prevent Loop Stream Detector(LSD) from engaging
+ * and not clearing the branch history. The call tree looks like:
+ *
+ * call 1
+ * call 2
+ * call 2
+ * call 2
+ * call 2
+ * call 2
+ * ret
+ * ret
+ * ret
+ * ret
+ * ret
+ * ret
+ *
+ * This means that the stack is non-constant and ORC can't unwind it with %rsp
+ * alone. Therefore we unconditionally set up the frame pointer, which allows
+ * ORC to unwind properly.
+ *
+ * The alignment is for performance and not for safety, and may be safely
+ * refactored in the future if needed.
+ */
+SYM_FUNC_START(clear_bhb_loop)
+ push %rbp
+ mov %rsp, %rbp
+ movl $5, %ecx
+ ANNOTATE_INTRA_FUNCTION_CALL
+ call 1f
+ jmp 5f
+ .align 64, 0xcc
+ ANNOTATE_INTRA_FUNCTION_CALL
+1: call 2f
+ RET
+ .align 64, 0xcc
+2: movl $5, %eax
+3: jmp 4f
+ nop
+4: sub $1, %eax
+ jnz 3b
+ sub $1, %ecx
+ jnz 1b
+ RET
+5: lfence
+ pop %rbp
+ RET
+SYM_FUNC_END(clear_bhb_loop)
+EXPORT_SYMBOL_GPL(clear_bhb_loop)
+STACK_FRAME_NON_STANDARD(clear_bhb_loop)