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[2a01:238:4383:600:38bc:a715:4b6d:a889]) by mx.google.com with ESMTPS id r12si728614edk.456.2018.03.05.02.26.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 05 Mar 2018 02:26:12 -0800 (PST) From: Joerg Roedel Subject: [PATCH 09/34] x86/entry/32: Leave the kernel via trampoline stack Date: Mon, 5 Mar 2018 11:25:38 +0100 Message-Id: <1520245563-8444-10-git-send-email-joro@8bytes.org> In-Reply-To: <1520245563-8444-1-git-send-email-joro@8bytes.org> References: <1520245563-8444-1-git-send-email-joro@8bytes.org> Sender: owner-linux-mm@kvack.org List-ID: To: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Andy Lutomirski , Dave Hansen , Josh Poimboeuf , Juergen Gross , Peter Zijlstra , Borislav Petkov , Jiri Kosina , Boris Ostrovsky , Brian Gerst , David Laight , Denys Vlasenko , Eduardo Valentin , Greg KH , Will Deacon , aliguori@amazon.com, daniel.gruss@iaik.tugraz.at, hughd@google.com, keescook@google.com, Andrea Arcangeli , Waiman Long , Pavel Machek , jroedel@suse.de, joro@8bytes.org From: Joerg Roedel Switch back to the trampoline stack before returning to userspace. Signed-off-by: Joerg Roedel --- arch/x86/entry/entry_32.S | 79 +++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 77 insertions(+), 2 deletions(-) diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 1737da2..1b5656d 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -339,6 +339,60 @@ .endm /* + * Switch back from the kernel stack to the entry stack. + * + * The %esp register must point to pt_regs on the task stack. It will + * first calculate the size of the stack-frame to copy, depending on + * whether we return to VM86 mode or not. With that it uses 'rep movsl' + * to copy the contents of the stack over to the entry stack. + * + * We must be very careful here, as we can't trust the contents of the + * task-stack once we switched to the entry-stack. When an NMI happens + * while on the entry-stack, the NMI handler will switch back to the top + * of the task stack, overwriting our stack-frame we are about to copy. + * Therefore we switch the stack only after everything is copied over. + */ +.macro SWITCH_TO_ENTRY_STACK + + ALTERNATIVE "", "jmp .Lend_\@", X86_FEATURE_XENPV + + /* Bytes to copy */ + movl $PTREGS_SIZE, %ecx + +#ifdef CONFIG_VM86 + testl $(X86_EFLAGS_VM), PT_EFLAGS(%esp) + jz .Lcopy_pt_regs_\@ + + /* Additional 4 registers to copy when returning to VM86 mode */ + addl $(4 * 4), %ecx + +.Lcopy_pt_regs_\@: +#endif + + /* Initialize source and destination for movsb */ + movl PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %edi + subl %ecx, %edi + movl %esp, %esi + + /* Save future stack pointer in %ebx */ + movl %edi, %ebx + + /* Copy over the stack-frame */ + shrl $2, %ecx + cld + rep movsl + + /* + * Switch to entry-stack - needs to happen after everything is + * copied because the NMI handler will overwrite the task-stack + * when on entry-stack + */ + movl %ebx, %esp + +.Lend_\@: +.endm + +/* * %eax: prev task * %edx: next task */ @@ -579,25 +633,45 @@ ENTRY(entry_SYSENTER_32) /* Opportunistic SYSEXIT */ TRACE_IRQS_ON /* User mode traces as IRQs on. */ + + /* + * Setup entry stack - we keep the pointer in %eax and do the + * switch after almost all user-state is restored. + */ + + /* Load entry stack pointer and allocate frame for eflags/eax */ + movl PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %eax + subl $(2*4), %eax + + /* Copy eflags and eax to entry stack */ + movl PT_EFLAGS(%esp), %edi + movl PT_EAX(%esp), %esi + movl %edi, (%eax) + movl %esi, 4(%eax) + + /* Restore user registers and segments */ movl PT_EIP(%esp), %edx /* pt_regs->ip */ movl PT_OLDESP(%esp), %ecx /* pt_regs->sp */ 1: mov PT_FS(%esp), %fs PTGS_TO_GS + popl %ebx /* pt_regs->bx */ addl $2*4, %esp /* skip pt_regs->cx and pt_regs->dx */ popl %esi /* pt_regs->si */ popl %edi /* pt_regs->di */ popl %ebp /* pt_regs->bp */ - popl %eax /* pt_regs->ax */ + + /* Switch to entry stack */ + movl %eax, %esp /* * Restore all flags except IF. (We restore IF separately because * STI gives a one-instruction window in which we won't be interrupted, * whereas POPF does not.) */ - addl $PT_EFLAGS-PT_DS, %esp /* point esp at pt_regs->flags */ btr $X86_EFLAGS_IF_BIT, (%esp) popfl + popl %eax /* * Return back to the vDSO, which will pop ecx and edx. @@ -666,6 +740,7 @@ ENTRY(entry_INT80_32) restore_all: TRACE_IRQS_IRET + SWITCH_TO_ENTRY_STACK .Lrestore_all_notrace: CHECK_AND_APPLY_ESPFIX .Lrestore_nocheck: -- 2.7.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org