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x86/entry: Harden return-to-user
Make the CONFIG_DEBUG_ENTRY=y check that validates CS is a user segment unconditional and move it nearer to IRET. PRE: 140,026,608 cycles:k ( +- 0.01% ) 236,696,176 instructions:k # 1.69 insn per cycle ( +- 0.00% ) POST: 139,957,681 cycles:k ( +- 0.01% ) 236,681,819 instructions:k # 1.69 insn per cycle ( +- 0.00% ) (this is with --repeat 100 and the run-to-run variance is bigger than the difference shown) Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/r/20231120143626.753200755@infradead.org
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parent
c516213726
commit
1e4d3001f5
1 changed files with 8 additions and 10 deletions
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@ -559,13 +559,6 @@ __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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jnz 1f
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ud2
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1:
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#endif
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#ifdef CONFIG_XEN_PV
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ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
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#endif
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@ -576,8 +569,14 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
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STACKLEAK_ERASE
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POP_REGS
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add $8, %rsp /* orig_ax */
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UNWIND_HINT_IRET_REGS
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.Lswapgs_and_iret:
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swapgs
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jmp .Lnative_iret
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/* Assert that the IRET frame indicates user mode. */
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testb $3, 8(%rsp)
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jnz .Lnative_iret
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ud2
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#ifdef CONFIG_PAGE_TABLE_ISOLATION
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.Lpti_restore_regs_and_return_to_usermode:
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@ -613,8 +612,7 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
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/* Restore RDI. */
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popq %rdi
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swapgs
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jmp .Lnative_iret
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jmp .Lswapgs_and_iret
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#endif
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SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL)
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