Date: Mon, 12 Feb 2018 07:27:40 -0800 (PST) From: "Rodney W. Grimes" <freebsd@pdx.rh.CN85.dnsmgr.net> To: Tycho Nightingale <tychon@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r329162 - in head/sys/amd64/vmm: amd intel Message-ID: <201802121527.w1CFRe3K044500@pdx.rh.CN85.dnsmgr.net> In-Reply-To: <201802121445.w1CEjR3n082516@repo.freebsd.org>
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> Author: tychon > Date: Mon Feb 12 14:45:27 2018 > New Revision: 329162 > URL: https://svnweb.freebsd.org/changeset/base/329162 > > Log: > Provide further mitigation against CVE-2017-5715 by flushing the > return stack buffer (RSB) upon returning from the guest. > > This was inspired by this linux commit: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/x86/kvm?id=117cc7a908c83697b0b737d15ae1eb5943afe35b > > Reviewed by: grehan > Sponsored by: Dell EMC Isilon > Differential Revision: https://reviews.freebsd.org/D14272 Plans to MFC this? It would be good to have as many meltdown/spectre patches as possible in the upcomming 11.2 release. > Modified: > head/sys/amd64/vmm/amd/svm_support.S > head/sys/amd64/vmm/intel/vmcs.c > head/sys/amd64/vmm/intel/vmx.h > head/sys/amd64/vmm/intel/vmx_support.S > > Modified: head/sys/amd64/vmm/amd/svm_support.S > ============================================================================== > --- head/sys/amd64/vmm/amd/svm_support.S Mon Feb 12 14:44:21 2018 (r329161) > +++ head/sys/amd64/vmm/amd/svm_support.S Mon Feb 12 14:45:27 2018 (r329162) > @@ -113,6 +113,23 @@ ENTRY(svm_launch) > movq %rdi, SCTX_RDI(%rax) > movq %rsi, SCTX_RSI(%rax) > > + /* > + * To prevent malicious branch target predictions from > + * affecting the host, overwrite all entries in the RSB upon > + * exiting a guest. > + */ > + mov $16, %ecx /* 16 iterations, two calls per loop */ > + mov %rsp, %rax > +0: call 2f /* create an RSB entry. */ > +1: pause > + call 1b /* capture rogue speculation. */ > +2: call 2f /* create an RSB entry. */ > +1: pause > + call 1b /* capture rogue speculation. */ > +2: sub $1, %ecx > + jnz 0b > + mov %rax, %rsp > + > /* Restore host state */ > pop %r15 > pop %r14 > > Modified: head/sys/amd64/vmm/intel/vmcs.c > ============================================================================== > --- head/sys/amd64/vmm/intel/vmcs.c Mon Feb 12 14:44:21 2018 (r329161) > +++ head/sys/amd64/vmm/intel/vmcs.c Mon Feb 12 14:45:27 2018 (r329162) > @@ -34,6 +34,7 @@ > __FBSDID("$FreeBSD$"); > > #include <sys/param.h> > +#include <sys/sysctl.h> > #include <sys/systm.h> > #include <sys/pcpu.h> > > @@ -52,6 +53,12 @@ __FBSDID("$FreeBSD$"); > #include <ddb/ddb.h> > #endif > > +SYSCTL_DECL(_hw_vmm_vmx); > + > +static int no_flush_rsb; > +SYSCTL_INT(_hw_vmm_vmx, OID_AUTO, no_flush_rsb, CTLFLAG_RW, > + &no_flush_rsb, 0, "Do not flush RSB upon vmexit"); > + > static uint64_t > vmcs_fix_regval(uint32_t encoding, uint64_t val) > { > @@ -403,8 +410,15 @@ vmcs_init(struct vmcs *vmcs) > goto done; > > /* instruction pointer */ > - if ((error = vmwrite(VMCS_HOST_RIP, (u_long)vmx_exit_guest)) != 0) > - goto done; > + if (no_flush_rsb) { > + if ((error = vmwrite(VMCS_HOST_RIP, > + (u_long)vmx_exit_guest)) != 0) > + goto done; > + } else { > + if ((error = vmwrite(VMCS_HOST_RIP, > + (u_long)vmx_exit_guest_flush_rsb)) != 0) > + goto done; > + } > > /* link pointer */ > if ((error = vmwrite(VMCS_LINK_POINTER, ~0)) != 0) > > Modified: head/sys/amd64/vmm/intel/vmx.h > ============================================================================== > --- head/sys/amd64/vmm/intel/vmx.h Mon Feb 12 14:44:21 2018 (r329161) > +++ head/sys/amd64/vmm/intel/vmx.h Mon Feb 12 14:45:27 2018 (r329162) > @@ -150,5 +150,6 @@ u_long vmx_fix_cr4(u_long cr4); > int vmx_set_tsc_offset(struct vmx *vmx, int vcpu, uint64_t offset); > > extern char vmx_exit_guest[]; > +extern char vmx_exit_guest_flush_rsb[]; > > #endif > > Modified: head/sys/amd64/vmm/intel/vmx_support.S > ============================================================================== > --- head/sys/amd64/vmm/intel/vmx_support.S Mon Feb 12 14:44:21 2018 (r329161) > +++ head/sys/amd64/vmm/intel/vmx_support.S Mon Feb 12 14:45:27 2018 (r329162) > @@ -42,6 +42,29 @@ > #define VLEAVE pop %rbp > > /* > + * Save the guest context. > + */ > +#define VMX_GUEST_SAVE \ > + movq %rdi,VMXCTX_GUEST_RDI(%rsp); \ > + movq %rsi,VMXCTX_GUEST_RSI(%rsp); \ > + movq %rdx,VMXCTX_GUEST_RDX(%rsp); \ > + movq %rcx,VMXCTX_GUEST_RCX(%rsp); \ > + movq %r8,VMXCTX_GUEST_R8(%rsp); \ > + movq %r9,VMXCTX_GUEST_R9(%rsp); \ > + movq %rax,VMXCTX_GUEST_RAX(%rsp); \ > + movq %rbx,VMXCTX_GUEST_RBX(%rsp); \ > + movq %rbp,VMXCTX_GUEST_RBP(%rsp); \ > + movq %r10,VMXCTX_GUEST_R10(%rsp); \ > + movq %r11,VMXCTX_GUEST_R11(%rsp); \ > + movq %r12,VMXCTX_GUEST_R12(%rsp); \ > + movq %r13,VMXCTX_GUEST_R13(%rsp); \ > + movq %r14,VMXCTX_GUEST_R14(%rsp); \ > + movq %r15,VMXCTX_GUEST_R15(%rsp); \ > + movq %cr2,%rdi; \ > + movq %rdi,VMXCTX_GUEST_CR2(%rsp); \ > + movq %rsp,%rdi; > + > +/* > * Assumes that %rdi holds a pointer to the 'vmxctx'. > * > * On "return" all registers are updated to reflect guest state. The two > @@ -211,31 +234,55 @@ inst_error: > * The VMCS-restored %rsp points to the struct vmxctx > */ > ALIGN_TEXT > - .globl vmx_exit_guest > -vmx_exit_guest: > + .globl vmx_exit_guest_flush_rsb > +vmx_exit_guest_flush_rsb: > /* > * Save guest state that is not automatically saved in the vmcs. > */ > - movq %rdi,VMXCTX_GUEST_RDI(%rsp) > - movq %rsi,VMXCTX_GUEST_RSI(%rsp) > - movq %rdx,VMXCTX_GUEST_RDX(%rsp) > - movq %rcx,VMXCTX_GUEST_RCX(%rsp) > - movq %r8,VMXCTX_GUEST_R8(%rsp) > - movq %r9,VMXCTX_GUEST_R9(%rsp) > - movq %rax,VMXCTX_GUEST_RAX(%rsp) > - movq %rbx,VMXCTX_GUEST_RBX(%rsp) > - movq %rbp,VMXCTX_GUEST_RBP(%rsp) > - movq %r10,VMXCTX_GUEST_R10(%rsp) > - movq %r11,VMXCTX_GUEST_R11(%rsp) > - movq %r12,VMXCTX_GUEST_R12(%rsp) > - movq %r13,VMXCTX_GUEST_R13(%rsp) > - movq %r14,VMXCTX_GUEST_R14(%rsp) > - movq %r15,VMXCTX_GUEST_R15(%rsp) > + VMX_GUEST_SAVE > > - movq %cr2,%rdi > - movq %rdi,VMXCTX_GUEST_CR2(%rsp) > + /* > + * Deactivate guest pmap from this cpu. > + */ > + movq VMXCTX_PMAP(%rdi), %r11 > + movl PCPU(CPUID), %r10d > + LK btrl %r10d, PM_ACTIVE(%r11) > > - movq %rsp,%rdi > + VMX_HOST_RESTORE > + > + VMX_GUEST_CLOBBER > + > + /* > + * To prevent malicious branch target predictions from > + * affecting the host, overwrite all entries in the RSB upon > + * exiting a guest. > + */ > + mov $16, %ecx /* 16 iterations, two calls per loop */ > + mov %rsp, %rax > +0: call 2f /* create an RSB entry. */ > +1: pause > + call 1b /* capture rogue speculation. */ > +2: call 2f /* create an RSB entry. */ > +1: pause > + call 1b /* capture rogue speculation. */ > +2: sub $1, %ecx > + jnz 0b > + mov %rax, %rsp > + > + /* > + * This will return to the caller of 'vmx_enter_guest()' with a return > + * value of VMX_GUEST_VMEXIT. > + */ > + movl $VMX_GUEST_VMEXIT, %eax > + VLEAVE > + ret > + > + .globl vmx_exit_guest > +vmx_exit_guest: > + /* > + * Save guest state that is not automatically saved in the vmcs. > + */ > + VMX_GUEST_SAVE > > /* > * Deactivate guest pmap from this cpu. > > -- Rod Grimes rgrimes@freebsd.org
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