Date: Wed, 18 May 2011 02:03:07 +0200 From: Oliver Pinter <oliver.pntr@gmail.com> To: freebsd-hackers@freebsd.org Subject: Fwd: [PATCH v2 3/4] x86, head_32/64.S: Enable SMEP Message-ID: <BANLkTi=ij7n8qiZ=n7mtUB5uZP-T6S1uRw@mail.gmail.com> In-Reply-To: <1305581685-5144-4-git-send-email-fenghua.yu@intel.com> References: <1305581685-5144-1-git-send-email-fenghua.yu@intel.com> <1305581685-5144-4-git-send-email-fenghua.yu@intel.com>
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---------- Forwarded message ---------- From: Fenghua Yu <fenghua.yu@intel.com> Date: Mon, 16 May 2011 14:34:44 -0700 Subject: [PATCH v2 3/4] x86, head_32/64.S: Enable SMEP To: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>, H Peter Anvin <hpa@zytor.com>, Asit K Mallick <asit.k.mallick@intel.com>, Linus Torvalds <torvalds@linux-foundation.org>, Avi Kivity <avi@redhat.com>, Arjan van de Ven <arjan@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Andi Kleen <andi@firstfloor.org> Cc: linux-kernel <linux-kernel@vger.kernel.org>, Fenghua Yu <fenghua.yu@intel.com> From: Fenghua Yu <fenghua.yu@intel.com> Enable newly documented SMEP (Supervisor Mode Execution Protection) CPU feature in kernel. SMEP prevents the CPU in kernel-mode to jump to an executable page that does not have the kernel/system flag set in the pte. This prevents the kernel from executing user-space code accidentally or maliciously, so it for example prevents kernel exploits from jumping to specially prepared user-mode shell code. The violation will cause page fault #PF and will have error code identical to XD violation. CR4.SMEP (bit 20) is 0 at power-on. If the feature is supported by CPU (X86_FEATURE_SMEP), enable SMEP by setting CR4.SMEP. New kernel option nosmep disables the feature even if the feature is supported by CPU. Signed-off-by: Fenghua Yu <fenghua.yu@intel.com> --- arch/x86/kernel/head_32.S | 17 +++++++++++++---- arch/x86/kernel/head_64.S | 13 +++++++++++-- 2 files changed, 24 insertions(+), 6 deletions(-) diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S index ce0be7c..5325c02 100644 --- a/arch/x86/kernel/head_32.S +++ b/arch/x86/kernel/head_32.S @@ -308,11 +308,20 @@ default_entry: movl cr4_bits,%edx andl %edx,%edx jz 6f - movl %cr4,%eax # Turn on paging options (PSE,PAE,..) - orl %edx,%eax - movl %eax,%cr4 + movl %cr4,%edi # Turn on paging options (PSE,PAE,..) + orl %edx,%edi - testb $X86_CR4_PAE, %al # check if PAE is enabled + /* Check if SMEP is supported by the processor */ + movl $0x7, %eax + movl $0, %ecx + cpuid + btl $7, %ebx + jnc 1f + /* Enable SMEP */ + orl $(X86_CR4_SMEP), %edi +1: movl %edi, %cr4 + + test $X86_CR4_PAE, %di # check if PAE is enabled jz 6f /* Check if extended functions are implemented */ diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index e11e394..220ec5f 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -161,8 +161,17 @@ ENTRY(secondary_startup_64) */ /* Enable PAE mode and PGE */ - movl $(X86_CR4_PAE | X86_CR4_PGE), %eax - movq %rax, %cr4 + movl $(X86_CR4_PAE | X86_CR4_PGE), %edi + + /* Check if SMEP is supported by the processor */ + movl $0x7, %eax + movl $0, %ecx + cpuid + btl $7, %ebx + jnc 1f + /* Enable PAE mode, PGE, and SMEP */ + movl $(X86_CR4_PAE | X86_CR4_PGE | X86_CR4_SMEP), %edi +1: movq %rdi, %cr4 /* Setup early boot stage 4 level pagetables. */ movq $(init_level4_pgt - __START_KERNEL_map), %rax -- 1.7.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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