From 8c7aa698baca5e8f1ba9edb68081f1e7a1abf455 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 1 Oct 2014 11:49:04 -0700 Subject: x86_64, entry: Filter RFLAGS.NT on entry from userspace The NT flag doesn't do anything in long mode other than causing IRET to #GP. Oddly, CPL3 code can still set NT using popf. Entry via hardware or software interrupt clears NT automatically, so the only relevant entries are fast syscalls. If user code causes kernel code to run with NT set, then there's at least some (small) chance that it could cause trouble. For example, user code could cause a call to EFI code with NT set, and who knows what would happen? Apparently some games on Wine sometimes do this (!), and, if an IRET return happens, they will segfault. That segfault cannot be handled, because signal delivery fails, too. This patch programs the CPU to clear NT on entry via SYSCALL (both 32-bit and 64-bit, by my reading of the AMD APM), and it clears NT in software on entry via SYSENTER. To save a few cycles, this borrows a trick from Jan Beulich in Xen: it checks whether NT is set before trying to clear it. As a result, it seems to have very little effect on SYSENTER performance on my machine. There's another minor bug fix in here: it looks like the CFI annotations were wrong if CONFIG_AUDITSYSCALL=n. Testers beware: on Xen, SYSENTER with NT set turns into a GPF. I haven't touched anything on 32-bit kernels. The syscall mask change comes from a variant of this patch by Anish Bhatt. Note to stable maintainers: there is no known security issue here. A misguided program can set NT and cause the kernel to try and fail to deliver SIGSEGV, crashing the program. This patch fixes Far Cry on Wine: https://bugs.winehq.org/show_bug.cgi?id=33275 Cc: Reported-by: Anish Bhatt Signed-off-by: Andy Lutomirski Link: http://lkml.kernel.org/r/395749a5d39a29bd3e4b35899cf3a3c1340e5595.1412189265.git.luto@amacapital.net Signed-off-by: H. Peter Anvin --- arch/x86/kernel/cpu/common.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index e4ab2b42bd6f..31265580c38a 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1184,7 +1184,7 @@ void syscall_init(void) /* Flags to clear on syscall */ wrmsrl(MSR_SYSCALL_MASK, X86_EFLAGS_TF|X86_EFLAGS_DF|X86_EFLAGS_IF| - X86_EFLAGS_IOPL|X86_EFLAGS_AC); + X86_EFLAGS_IOPL|X86_EFLAGS_AC|X86_EFLAGS_NT); } /* -- cgit v1.2.3 From 2dee5c43da3a981489a4f18972827139afcbee82 Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Wed, 24 Sep 2014 06:32:19 +0200 Subject: x86: Fix section conflict for numachip A variable cannot be both __read_mostly and const. This is a meaningless combination. Just make it only const. This fixes the LTO build with numachip enabled. Signed-off-by: Andi Kleen Link: http://lkml.kernel.org/r/1411533139-25708-1-git-send-email-andi@firstfloor.org Signed-off-by: Thomas Gleixner --- arch/x86/kernel/apic/apic_numachip.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/apic/apic_numachip.c b/arch/x86/kernel/apic/apic_numachip.c index ae915391ebec..4128b5fcb559 100644 --- a/arch/x86/kernel/apic/apic_numachip.c +++ b/arch/x86/kernel/apic/apic_numachip.c @@ -32,7 +32,7 @@ static int numachip_system __read_mostly; -static const struct apic apic_numachip __read_mostly; +static const struct apic apic_numachip; static unsigned int get_apic_id(unsigned long x) { -- cgit v1.2.3