From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 2 Nov 2017 00:59:00 -0700 Subject: [PATCH] x86/entry/64: Move SWAPGS into the common IRET-to-usermode path MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit CVE-2017-5754 All of the code paths that ended up doing IRET to usermode did SWAPGS immediately beforehand. Move the SWAPGS into the common code. Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/27fd6f45b7cd640de38fb9066fd0349bcd11f8e1.1509609304.git.luto@kernel.org Signed-off-by: Ingo Molnar (cherry picked from commit 8a055d7f411d41755ce30db5bb65b154777c4b78) Signed-off-by: Andy Whitcroft Signed-off-by: Kleber Sacilotto de Souza (cherry picked from commit 62a85594f9be3baeb2495089f1c2980bc497d03b) Signed-off-by: Fabian Grünbichler --- arch/x86/entry/entry_64.S | 32 ++++++++++++++------------------ arch/x86/entry/entry_64_compat.S | 3 +-- 2 files changed, 15 insertions(+), 20 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index e546441fbec3..7c8258e3ad2d 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -249,12 +249,14 @@ return_from_SYSCALL_64: /* * Try to use SYSRET instead of IRET if we're returning to - * a completely clean 64-bit userspace context. + * a completely clean 64-bit userspace context. If we're not, + * go to the slow exit path. */ movq RCX(%rsp), %rcx movq RIP(%rsp), %r11 - cmpq %rcx, %r11 /* RCX == RIP */ - jne opportunistic_sysret_failed + + cmpq %rcx, %r11 /* SYSRET requires RCX == RIP */ + jne swapgs_restore_regs_and_return_to_usermode /* * On Intel CPUs, SYSRET with non-canonical RCX/RIP will #GP @@ -272,14 +274,14 @@ return_from_SYSCALL_64: /* If this changed %rcx, it was not canonical */ cmpq %rcx, %r11 - jne opportunistic_sysret_failed + jne swapgs_restore_regs_and_return_to_usermode cmpq $__USER_CS, CS(%rsp) /* CS must match SYSRET */ - jne opportunistic_sysret_failed + jne swapgs_restore_regs_and_return_to_usermode movq R11(%rsp), %r11 cmpq %r11, EFLAGS(%rsp) /* R11 == RFLAGS */ - jne opportunistic_sysret_failed + jne swapgs_restore_regs_and_return_to_usermode /* * SYSCALL clears RF when it saves RFLAGS in R11 and SYSRET cannot @@ -300,12 +302,12 @@ return_from_SYSCALL_64: * would never get past 'stuck_here'. */ testq $(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11 - jnz opportunistic_sysret_failed + jnz swapgs_restore_regs_and_return_to_usermode /* nothing to check for RSP */ cmpq $__USER_DS, SS(%rsp) /* SS must match SYSRET */ - jne opportunistic_sysret_failed + jne swapgs_restore_regs_and_return_to_usermode /* * We win! This label is here just for ease of understanding @@ -318,10 +320,6 @@ syscall_return_via_sysret: movq RSP(%rsp), %rsp UNWIND_HINT_EMPTY USERGS_SYSRET64 - -opportunistic_sysret_failed: - SWAPGS - jmp restore_regs_and_return_to_usermode END(entry_SYSCALL_64) ENTRY(stub_ptregs_64) @@ -422,8 +420,7 @@ ENTRY(ret_from_fork) movq %rsp, %rdi call syscall_return_slowpath /* returns with IRQs disabled */ TRACE_IRQS_ON /* user mode is traced as IRQS on */ - SWAPGS - jmp restore_regs_and_return_to_usermode + jmp swapgs_restore_regs_and_return_to_usermode 1: /* kernel thread */ @@ -611,9 +608,8 @@ GLOBAL(retint_user) mov %rsp,%rdi call prepare_exit_to_usermode TRACE_IRQS_IRETQ - SWAPGS -GLOBAL(restore_regs_and_return_to_usermode) +GLOBAL(swapgs_restore_regs_and_return_to_usermode) #ifdef CONFIG_DEBUG_ENTRY /* Assert that pt_regs indicates user mode. */ testl $3, CS(%rsp) @@ -621,6 +617,7 @@ GLOBAL(restore_regs_and_return_to_usermode) ud2 1: #endif + SWAPGS RESTORE_EXTRA_REGS RESTORE_C_REGS REMOVE_PT_GPREGS_FROM_STACK 8 @@ -1355,8 +1352,7 @@ ENTRY(nmi) * Return back to user mode. We must *not* do the normal exit * work, because we don't want to enable interrupts. */ - SWAPGS - jmp restore_regs_and_return_to_usermode + jmp swapgs_restore_regs_and_return_to_usermode .Lnmi_from_kernel: /* diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index 2b3a88feaa2b..be745b7a3e3e 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -336,8 +336,7 @@ ENTRY(entry_INT80_compat) /* Go back to user mode. */ TRACE_IRQS_ON - SWAPGS - jmp restore_regs_and_return_to_usermode + jmp swapgs_restore_regs_and_return_to_usermode END(entry_INT80_compat) ALIGN -- 2.14.2