| From | Andy Lutomirski <> | Subject | [PATCH v2 07/36] x86/entry/64/compat: After SYSENTER, move STI after the NT fixup | Date | Mon, 5 Oct 2015 17:47:55 -0700 |
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We eventually want to make it all the way into C code before enabling interrupts. We need to rework our flags handling slightly to delay enabling interrupts.
Signed-off-by: Andy Lutomirski <luto@kernel.org> --- arch/x86/entry/entry_64_compat.S | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-)
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index aa76864a8a6b..1432d60a1f4a 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -58,14 +58,9 @@ ENDPROC(native_usergs_sysret32) * with the int 0x80 path. */ ENTRY(entry_SYSENTER_compat) - /* - * Interrupts are off on entry. - * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON, - * it is too small to ever cause noticeable irq latency. - */ + /* Interrupts are off on entry. */ SWAPGS_UNSAFE_STACK movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp - ENABLE_INTERRUPTS(CLBR_NONE) /* Zero-extending 32-bit regs, do not remove */ movl %ebp, %ebp @@ -76,7 +71,16 @@ ENTRY(entry_SYSENTER_compat) /* Construct struct pt_regs on stack */ pushq $__USER32_DS /* pt_regs->ss */ pushq %rbp /* pt_regs->sp */ - pushfq /* pt_regs->flags */ + + /* + * Push flags. This is nasty. First, interrupts are currently + * off, but we need pt_regs->flags to have IF set. Second, even + * if TF was set when SYSENTER started, it's clear by now. We fix + * that later using TIF_SINGLESTEP. + */ + pushfq /* pt_regs->flags (except IF = 0) */ + orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */ + pushq $__USER32_CS /* pt_regs->cs */ pushq %r10 /* pt_regs->ip = thread_info->sysenter_return */ pushq %rax /* pt_regs->orig_ax */ @@ -92,12 +96,22 @@ ENTRY(entry_SYSENTER_compat) * Sysenter doesn't filter flags, so we need to clear NT * ourselves. To save a few cycles, we can check whether * NT was set instead of doing an unconditional popfq. + * This needs to happen before enabling interrupts so that + * we don't get preempted with NT set. */ testl $X86_EFLAGS_NT, EFLAGS(%rsp) jnz sysenter_fix_flags sysenter_flags_fixed: /* + * Re-enable interrupts. IRQ tracing already thinks that IRQs are + * on (since we treat user mode as having IRQs on), and the + * prologue above is too short for it to be worth adding a + * tracing round trip. + */ + ENABLE_INTERRUPTS(CLBR_NONE) + + /* * no need to do an access_ok check here because rbp has been * 32-bit zero extended */ @@ -244,7 +258,7 @@ sysexit_audit: #endif sysenter_fix_flags: - pushq $(X86_EFLAGS_IF|X86_EFLAGS_FIXED) + pushq $X86_EFLAGS_FIXED popfq jmp sysenter_flags_fixed -- 2.4.3
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