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Mon, 09 Nov 2020 11:21:40 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0A9BKlY7147282; Mon, 9 Nov 2020 11:21:40 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserp3020.oracle.com with ESMTP id 34p5fxjve8-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 09 Nov 2020 11:21:40 +0000 Received: from abhmp0018.oracle.com (abhmp0018.oracle.com [141.146.116.24]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 0A9BLbVf028764; Mon, 9 Nov 2020 11:21:38 GMT Received: from linux.home (/92.157.91.83) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 09 Nov 2020 03:21:37 -0800 From: Alexandre Chartre To: "tglx@linutronix.de"@userv0121.oracle.com, "mingo@redhat.com"@userv0121.oracle.com, "bp@alien8.de"@userv0121.oracle.com, "hpa@zytor.com"@userv0121.oracle.com, "x86@kernel.org"@userv0121.oracle.com, "dave.hansen@linux.intel.com"@userv0121.oracle.com, "luto@kernel.org"@userv0121.oracle.com, "peterz@infradead.org"@userv0121.oracle.com, "linux-kernel@vger.kernel.org"@userv0121.oracle.com, "thomas.lendacky@amd.com"@userv0121.oracle.com, "jroedel@suse.de"@userv0121.oracle.com Cc: "konrad.wilk@oracle.com"@userv0121.oracle.com, "jan.setjeeilers@oracle.com"@userv0121.oracle.com, "junaids@google.com"@userv0121.oracle.com, "oweisse@google.com"@userv0121.oracle.com, "rppt@linux.vnet.ibm.com"@userv0121.oracle.com, "graf@amazon.de"@userv0121.oracle.com, "mgross@linux.intel.com"@userv0121.oracle.com, "kuzuno@gmail.com"@userv0121.oracle.com, "alexandre.chartre@oracle.com"@userv0121.oracle.com Subject: [RFC][PATCH 07/24] x86/entry: Fill ESPFIX stack using C code Date: Mon, 9 Nov 2020 12:23:02 +0100 Message-Id: <20201109112319.264511-8-alexandre.chartre@oracle.com> X-Mailer: git-send-email 2.18.4 In-Reply-To: <20201109112319.264511-1-alexandre.chartre@oracle.com> References: <20201109112319.264511-1-alexandre.chartre@oracle.com> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9799 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 spamscore=0 malwarescore=0 adultscore=0 phishscore=0 bulkscore=0 mlxlogscore=999 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011090075 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9799 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 priorityscore=1501 mlxscore=0 suspectscore=0 mlxlogscore=999 lowpriorityscore=0 spamscore=0 malwarescore=0 adultscore=0 clxscore=1015 bulkscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011090074 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The ESPFIX stack is filled using assembly code. Move this code to a C function so that it is easier to read and modify. Signed-off-by: Alexandre Chartre --- arch/x86/entry/entry_64.S | 62 ++++++++++++++++++------------------- arch/x86/kernel/espfix_64.c | 41 ++++++++++++++++++++++++ 2 files changed, 72 insertions(+), 31 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 73e9cd47dc83..6e0b5b010e0b 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -684,8 +684,10 @@ native_irq_return_ldt: * long (see ESPFIX_STACK_SIZE). espfix_waddr points to the bottom * of the ESPFIX stack. * - * We clobber RAX and RDI in this code. We stash RDI on the - * normal stack and RAX on the ESPFIX stack. + * We call into C code to fill the ESPFIX stack. We stash registers + * that the C function can clobber on the normal stack. The user RAX + * is stashed first so that it is adjacent to the iret frame which + * will be copied to the ESPFIX stack. * * The ESPFIX stack layout we set up looks like this: * @@ -699,39 +701,37 @@ native_irq_return_ldt: * --- bottom of ESPFIX stack --- */ - pushq %rdi /* Stash user RDI */ - SWAPGS /* to kernel GS */ - SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi /* to kernel CR3 */ - - movq PER_CPU_VAR(espfix_waddr), %rdi - movq %rax, (0*8)(%rdi) /* user RAX */ - movq (1*8)(%rsp), %rax /* user RIP */ - movq %rax, (1*8)(%rdi) - movq (2*8)(%rsp), %rax /* user CS */ - movq %rax, (2*8)(%rdi) - movq (3*8)(%rsp), %rax /* user RFLAGS */ - movq %rax, (3*8)(%rdi) - movq (5*8)(%rsp), %rax /* user SS */ - movq %rax, (5*8)(%rdi) - movq (4*8)(%rsp), %rax /* user RSP */ - movq %rax, (4*8)(%rdi) - /* Now RAX == RSP. */ - - andl $0xffff0000, %eax /* RAX = (RSP & 0xffff0000) */ + /* save registers */ + pushq %rax + pushq %rdi + pushq %rsi + pushq %rdx + pushq %rcx + pushq %r8 + pushq %r9 + pushq %r10 + pushq %r11 /* - * espfix_stack[31:16] == 0. The page tables are set up such that - * (espfix_stack | (X & 0xffff0000)) points to a read-only alias of - * espfix_waddr for any X. That is, there are 65536 RO aliases of - * the same page. Set up RSP so that RSP[31:16] contains the - * respective 16 bits of the /userspace/ RSP and RSP nonetheless - * still points to an RO alias of the ESPFIX stack. + * fill_espfix_stack will copy the iret+rax frame to the ESPFIX + * stack and return with RAX containing a pointer to the ESPFIX + * stack. */ - orq PER_CPU_VAR(espfix_stack), %rax + leaq 8*8(%rsp), %rdi /* points to the iret+rax frame */ + call fill_espfix_stack - SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi - SWAPGS /* to user GS */ - popq %rdi /* Restore user RDI */ + /* + * RAX contains a pointer to the ESPFIX, so restore registers but + * RAX. RAX will be restored from the ESPFIX stack. + */ + popq %r11 + popq %r10 + popq %r9 + popq %r8 + popq %rcx + popq %rdx + popq %rsi + popq %rdi movq %rax, %rsp UNWIND_HINT_IRET_REGS offset=8 diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c index 4fe7af58cfe1..6a81c4bd1542 100644 --- a/arch/x86/kernel/espfix_64.c +++ b/arch/x86/kernel/espfix_64.c @@ -33,6 +33,7 @@ #include #include #include +#include /* * Note: we only need 6*8 = 48 bytes for the espfix stack, but round @@ -205,3 +206,43 @@ void init_espfix_ap(int cpu) per_cpu(espfix_waddr, cpu) = (unsigned long)stack_page + (addr & ~PAGE_MASK); } + +/* + * iret frame with an additional user_rax register. + */ +struct iret_rax_frame { + unsigned long user_rax; + unsigned long rip; + unsigned long cs; + unsigned long rflags; + unsigned long rsp; + unsigned long ss; +}; + +noinstr unsigned long fill_espfix_stack(struct iret_rax_frame *frame) +{ + struct iret_rax_frame *espfix_frame; + unsigned long rsp; + + native_swapgs(); + switch_to_kernel_cr3(); + + espfix_frame = (struct iret_rax_frame *)this_cpu_read(espfix_waddr); + *espfix_frame = *frame; + + /* + * espfix_stack[31:16] == 0. The page tables are set up such that + * (espfix_stack | (X & 0xffff0000)) points to a read-only alias of + * espfix_waddr for any X. That is, there are 65536 RO aliases of + * the same page. Set up RSP so that RSP[31:16] contains the + * respective 16 bits of the /userspace/ RSP and RSP nonetheless + * still points to an RO alias of the ESPFIX stack. + */ + rsp = ((unsigned long)espfix_frame) & 0xffff0000; + rsp |= this_cpu_read(espfix_stack); + + switch_to_user_cr3(); + native_swapgs(); + + return rsp; +} -- 2.18.4