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linux/arch/mips/kvm/locore.S
James Hogan f798217dfd KVM: MIPS: Don't leak FPU/DSP to guest 
The FPU and DSP are enabled via the CP0 Status CU1 and MX bits by
kvm_mips_set_c0_status() on a guest exit, presumably in case there is
active state that needs saving if pre-emption occurs. However neither of
these bits are cleared again when returning to the guest.

This effectively gives the guest access to the FPU/DSP hardware after
the first guest exit even though it is not aware of its presence,
allowing FP instructions in guest user code to intermittently actually
execute instead of trapping into the guest OS for emulation. It will
then read & manipulate the hardware FP registers which technically
belong to the user process (e.g. QEMU), or are stale from another user
process. It can also crash the guest OS by causing an FP exception, for
which a guest exception handler won't have been registered.

First lets save and disable the FPU (and MSA) state with lose_fpu(1)
before entering the guest. This simplifies the problem, especially for
when guest FPU/MSA support is added in the future, and prevents FR=1 FPU
state being live when the FR bit gets cleared for the guest, which
according to the architecture causes the contents of the FPU and vector
registers to become UNPREDICTABLE.

We can then safely remove the enabling of the FPU in
kvm_mips_set_c0_status(), since there should never be any active FPU or
MSA state to save at pre-emption, which should plug the FPU leak.

DSP state is always live rather than being lazily restored, so for that
it is simpler to just clear the MX bit again when re-entering the guest.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Sanjay Lal <sanjayl@kymasys.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: kvm@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: <stable@vger.kernel.org> # v3.10+: 044f0f03ec: MIPS: KVM: Deliver guest interrupts
Cc: <stable@vger.kernel.org> # v3.10+
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-02-04 18:32:14 +01:00

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/*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Main entry point for the guest, exception handling.
*
* Copyright (C) 2012 MIPS Technologies, Inc. All rights reserved.
* Authors: Sanjay Lal <sanjayl@kymasys.com>
*/
#include <asm/asm.h>
#include <asm/asmmacro.h>
#include <asm/regdef.h>
#include <asm/mipsregs.h>
#include <asm/stackframe.h>
#include <asm/asm-offsets.h>
#define _C_LABEL(x) x
#define MIPSX(name) mips32_ ## name
#define CALLFRAME_SIZ 32
/*
* VECTOR
* exception vector entrypoint
*/
#define VECTOR(x, regmask) \
.ent _C_LABEL(x),0; \
EXPORT(x);
#define VECTOR_END(x) \
EXPORT(x);
/* Overload, Danger Will Robinson!! */
#define PT_HOST_ASID PT_BVADDR
#define PT_HOST_USERLOCAL PT_EPC
#define CP0_DDATA_LO $28,3
#define CP0_EBASE $15,1
#define CP0_INTCTL $12,1
#define CP0_SRSCTL $12,2
#define CP0_SRSMAP $12,3
#define CP0_HWRENA $7,0
/* Resume Flags */
#define RESUME_FLAG_HOST (1<<1) /* Resume host? */
#define RESUME_GUEST 0
#define RESUME_HOST RESUME_FLAG_HOST
/*
* __kvm_mips_vcpu_run: entry point to the guest
* a0: run
* a1: vcpu
*/
.set noreorder
.set noat
FEXPORT(__kvm_mips_vcpu_run)
/* k0/k1 not being used in host kernel context */
INT_ADDIU k1, sp, -PT_SIZE
LONG_S $0, PT_R0(k1)
LONG_S $1, PT_R1(k1)
LONG_S $2, PT_R2(k1)
LONG_S $3, PT_R3(k1)
LONG_S $4, PT_R4(k1)
LONG_S $5, PT_R5(k1)
LONG_S $6, PT_R6(k1)
LONG_S $7, PT_R7(k1)
LONG_S $8, PT_R8(k1)
LONG_S $9, PT_R9(k1)
LONG_S $10, PT_R10(k1)
LONG_S $11, PT_R11(k1)
LONG_S $12, PT_R12(k1)
LONG_S $13, PT_R13(k1)
LONG_S $14, PT_R14(k1)
LONG_S $15, PT_R15(k1)
LONG_S $16, PT_R16(k1)
LONG_S $17, PT_R17(k1)
LONG_S $18, PT_R18(k1)
LONG_S $19, PT_R19(k1)
LONG_S $20, PT_R20(k1)
LONG_S $21, PT_R21(k1)
LONG_S $22, PT_R22(k1)
LONG_S $23, PT_R23(k1)
LONG_S $24, PT_R24(k1)
LONG_S $25, PT_R25(k1)
/*
* XXXKYMA k0/k1 not saved, not being used if we got here through
* an ioctl()
*/
LONG_S $28, PT_R28(k1)
LONG_S $29, PT_R29(k1)
LONG_S $30, PT_R30(k1)
LONG_S $31, PT_R31(k1)
/* Save hi/lo */
mflo v0
LONG_S v0, PT_LO(k1)
mfhi v1
LONG_S v1, PT_HI(k1)
/* Save host status */
mfc0 v0, CP0_STATUS
LONG_S v0, PT_STATUS(k1)
/* Save host ASID, shove it into the BVADDR location */
mfc0 v1, CP0_ENTRYHI
andi v1, 0xff
LONG_S v1, PT_HOST_ASID(k1)
/* Save DDATA_LO, will be used to store pointer to vcpu */
mfc0 v1, CP0_DDATA_LO
LONG_S v1, PT_HOST_USERLOCAL(k1)
/* DDATA_LO has pointer to vcpu */
mtc0 a1, CP0_DDATA_LO
/* Offset into vcpu->arch */
INT_ADDIU k1, a1, VCPU_HOST_ARCH
/*
* Save the host stack to VCPU, used for exception processing
* when we exit from the Guest
*/
LONG_S sp, VCPU_HOST_STACK(k1)
/* Save the kernel gp as well */
LONG_S gp, VCPU_HOST_GP(k1)
/*
* Setup status register for running the guest in UM, interrupts
* are disabled
*/
li k0, (ST0_EXL | KSU_USER | ST0_BEV)
mtc0 k0, CP0_STATUS
ehb
/* load up the new EBASE */
LONG_L k0, VCPU_GUEST_EBASE(k1)
mtc0 k0, CP0_EBASE
/*
* Now that the new EBASE has been loaded, unset BEV, set
* interrupt mask as it was but make sure that timer interrupts
* are enabled
*/
li k0, (ST0_EXL | KSU_USER | ST0_IE)
andi v0, v0, ST0_IM
or k0, k0, v0
mtc0 k0, CP0_STATUS
ehb
/* Set Guest EPC */
LONG_L t0, VCPU_PC(k1)
mtc0 t0, CP0_EPC
FEXPORT(__kvm_mips_load_asid)
/* Set the ASID for the Guest Kernel */
INT_SLL t0, t0, 1 /* with kseg0 @ 0x40000000, kernel */
/* addresses shift to 0x80000000 */
bltz t0, 1f /* If kernel */
INT_ADDIU t1, k1, VCPU_GUEST_KERNEL_ASID /* (BD) */
INT_ADDIU t1, k1, VCPU_GUEST_USER_ASID /* else user */
1:
/* t1: contains the base of the ASID array, need to get the cpu id */
LONG_L t2, TI_CPU($28) /* smp_processor_id */
INT_SLL t2, t2, 2 /* x4 */
REG_ADDU t3, t1, t2
LONG_L k0, (t3)
andi k0, k0, 0xff
mtc0 k0, CP0_ENTRYHI
ehb
/* Disable RDHWR access */
mtc0 zero, CP0_HWRENA
/* Now load up the Guest Context from VCPU */
LONG_L $1, VCPU_R1(k1)
LONG_L $2, VCPU_R2(k1)
LONG_L $3, VCPU_R3(k1)
LONG_L $4, VCPU_R4(k1)
LONG_L $5, VCPU_R5(k1)
LONG_L $6, VCPU_R6(k1)
LONG_L $7, VCPU_R7(k1)
LONG_L $8, VCPU_R8(k1)
LONG_L $9, VCPU_R9(k1)
LONG_L $10, VCPU_R10(k1)
LONG_L $11, VCPU_R11(k1)
LONG_L $12, VCPU_R12(k1)
LONG_L $13, VCPU_R13(k1)
LONG_L $14, VCPU_R14(k1)
LONG_L $15, VCPU_R15(k1)
LONG_L $16, VCPU_R16(k1)
LONG_L $17, VCPU_R17(k1)
LONG_L $18, VCPU_R18(k1)
LONG_L $19, VCPU_R19(k1)
LONG_L $20, VCPU_R20(k1)
LONG_L $21, VCPU_R21(k1)
LONG_L $22, VCPU_R22(k1)
LONG_L $23, VCPU_R23(k1)
LONG_L $24, VCPU_R24(k1)
LONG_L $25, VCPU_R25(k1)
/* k0/k1 loaded up later */
LONG_L $28, VCPU_R28(k1)
LONG_L $29, VCPU_R29(k1)
LONG_L $30, VCPU_R30(k1)
LONG_L $31, VCPU_R31(k1)
/* Restore hi/lo */
LONG_L k0, VCPU_LO(k1)
mtlo k0
LONG_L k0, VCPU_HI(k1)
mthi k0
FEXPORT(__kvm_mips_load_k0k1)
/* Restore the guest's k0/k1 registers */
LONG_L k0, VCPU_R26(k1)
LONG_L k1, VCPU_R27(k1)
/* Jump to guest */
eret
VECTOR(MIPSX(exception), unknown)
/* Find out what mode we came from and jump to the proper handler. */
mtc0 k0, CP0_ERROREPC #01: Save guest k0
ehb #02:
mfc0 k0, CP0_EBASE #02: Get EBASE
INT_SRL k0, k0, 10 #03: Get rid of CPUNum
INT_SLL k0, k0, 10 #04
LONG_S k1, 0x3000(k0) #05: Save k1 @ offset 0x3000
INT_ADDIU k0, k0, 0x2000 #06: Exception handler is
# installed @ offset 0x2000
j k0 #07: jump to the function
nop #08: branch delay slot
VECTOR_END(MIPSX(exceptionEnd))
.end MIPSX(exception)
/*
* Generic Guest exception handler. We end up here when the guest
* does something that causes a trap to kernel mode.
*/
NESTED (MIPSX(GuestException), CALLFRAME_SIZ, ra)
/* Get the VCPU pointer from DDTATA_LO */
mfc0 k1, CP0_DDATA_LO
INT_ADDIU k1, k1, VCPU_HOST_ARCH
/* Start saving Guest context to VCPU */
LONG_S $0, VCPU_R0(k1)
LONG_S $1, VCPU_R1(k1)
LONG_S $2, VCPU_R2(k1)
LONG_S $3, VCPU_R3(k1)
LONG_S $4, VCPU_R4(k1)
LONG_S $5, VCPU_R5(k1)
LONG_S $6, VCPU_R6(k1)
LONG_S $7, VCPU_R7(k1)
LONG_S $8, VCPU_R8(k1)
LONG_S $9, VCPU_R9(k1)
LONG_S $10, VCPU_R10(k1)
LONG_S $11, VCPU_R11(k1)
LONG_S $12, VCPU_R12(k1)
LONG_S $13, VCPU_R13(k1)
LONG_S $14, VCPU_R14(k1)
LONG_S $15, VCPU_R15(k1)
LONG_S $16, VCPU_R16(k1)
LONG_S $17, VCPU_R17(k1)
LONG_S $18, VCPU_R18(k1)
LONG_S $19, VCPU_R19(k1)
LONG_S $20, VCPU_R20(k1)
LONG_S $21, VCPU_R21(k1)
LONG_S $22, VCPU_R22(k1)
LONG_S $23, VCPU_R23(k1)
LONG_S $24, VCPU_R24(k1)
LONG_S $25, VCPU_R25(k1)
/* Guest k0/k1 saved later */
LONG_S $28, VCPU_R28(k1)
LONG_S $29, VCPU_R29(k1)
LONG_S $30, VCPU_R30(k1)
LONG_S $31, VCPU_R31(k1)
/* We need to save hi/lo and restore them on the way out */
mfhi t0
LONG_S t0, VCPU_HI(k1)
mflo t0
LONG_S t0, VCPU_LO(k1)
/* Finally save guest k0/k1 to VCPU */
mfc0 t0, CP0_ERROREPC
LONG_S t0, VCPU_R26(k1)
/* Get GUEST k1 and save it in VCPU */
PTR_LI t1, ~0x2ff
mfc0 t0, CP0_EBASE
and t0, t0, t1
LONG_L t0, 0x3000(t0)
LONG_S t0, VCPU_R27(k1)
/* Now that context has been saved, we can use other registers */
/* Restore vcpu */
mfc0 a1, CP0_DDATA_LO
move s1, a1
/* Restore run (vcpu->run) */
LONG_L a0, VCPU_RUN(a1)
/* Save pointer to run in s0, will be saved by the compiler */
move s0, a0
/*
* Save Host level EPC, BadVaddr and Cause to VCPU, useful to
* process the exception
*/
mfc0 k0,CP0_EPC
LONG_S k0, VCPU_PC(k1)
mfc0 k0, CP0_BADVADDR
LONG_S k0, VCPU_HOST_CP0_BADVADDR(k1)
mfc0 k0, CP0_CAUSE
LONG_S k0, VCPU_HOST_CP0_CAUSE(k1)
mfc0 k0, CP0_ENTRYHI
LONG_S k0, VCPU_HOST_ENTRYHI(k1)
/* Now restore the host state just enough to run the handlers */
/* Swtich EBASE to the one used by Linux */
/* load up the host EBASE */
mfc0 v0, CP0_STATUS
.set at
or k0, v0, ST0_BEV
.set noat
mtc0 k0, CP0_STATUS
ehb
LONG_L k0, VCPU_HOST_EBASE(k1)
mtc0 k0,CP0_EBASE
/* Now that the new EBASE has been loaded, unset BEV and KSU_USER */
.set at
and v0, v0, ~(ST0_EXL | KSU_USER | ST0_IE)
or v0, v0, ST0_CU0
.set noat
mtc0 v0, CP0_STATUS
ehb
/* Load up host GP */
LONG_L gp, VCPU_HOST_GP(k1)
/* Need a stack before we can jump to "C" */
LONG_L sp, VCPU_HOST_STACK(k1)
/* Saved host state */
INT_ADDIU sp, sp, -PT_SIZE
/*
* XXXKYMA do we need to load the host ASID, maybe not because the
* kernel entries are marked GLOBAL, need to verify
*/
/* Restore host DDATA_LO */
LONG_L k0, PT_HOST_USERLOCAL(sp)
mtc0 k0, CP0_DDATA_LO
/* Restore RDHWR access */
PTR_LI k0, 0x2000000F
mtc0 k0, CP0_HWRENA
/* Jump to handler */
FEXPORT(__kvm_mips_jump_to_handler)
/*
* XXXKYMA: not sure if this is safe, how large is the stack??
* Now jump to the kvm_mips_handle_exit() to see if we can deal
* with this in the kernel
*/
PTR_LA t9, kvm_mips_handle_exit
jalr.hb t9
INT_ADDIU sp, sp, -CALLFRAME_SIZ /* BD Slot */
/* Return from handler Make sure interrupts are disabled */
di
ehb
/*
* XXXKYMA: k0/k1 could have been blown away if we processed
* an exception while we were handling the exception from the
* guest, reload k1
*/
move k1, s1
INT_ADDIU k1, k1, VCPU_HOST_ARCH
/*
* Check return value, should tell us if we are returning to the
* host (handle I/O etc)or resuming the guest
*/
andi t0, v0, RESUME_HOST
bnez t0, __kvm_mips_return_to_host
nop
__kvm_mips_return_to_guest:
/* Put the saved pointer to vcpu (s1) back into the DDATA_LO Register */
mtc0 s1, CP0_DDATA_LO
/* Load up the Guest EBASE to minimize the window where BEV is set */
LONG_L t0, VCPU_GUEST_EBASE(k1)
/* Switch EBASE back to the one used by KVM */
mfc0 v1, CP0_STATUS
.set at
or k0, v1, ST0_BEV
.set noat
mtc0 k0, CP0_STATUS
ehb
mtc0 t0, CP0_EBASE
/* Setup status register for running guest in UM */
.set at
or v1, v1, (ST0_EXL | KSU_USER | ST0_IE)
and v1, v1, ~(ST0_CU0 | ST0_MX)
.set noat
mtc0 v1, CP0_STATUS
ehb
/* Set Guest EPC */
LONG_L t0, VCPU_PC(k1)
mtc0 t0, CP0_EPC
/* Set the ASID for the Guest Kernel */
INT_SLL t0, t0, 1 /* with kseg0 @ 0x40000000, kernel */
/* addresses shift to 0x80000000 */
bltz t0, 1f /* If kernel */
INT_ADDIU t1, k1, VCPU_GUEST_KERNEL_ASID /* (BD) */
INT_ADDIU t1, k1, VCPU_GUEST_USER_ASID /* else user */
1:
/* t1: contains the base of the ASID array, need to get the cpu id */
LONG_L t2, TI_CPU($28) /* smp_processor_id */
INT_SLL t2, t2, 2 /* x4 */
REG_ADDU t3, t1, t2
LONG_L k0, (t3)
andi k0, k0, 0xff
mtc0 k0,CP0_ENTRYHI
ehb
/* Disable RDHWR access */
mtc0 zero, CP0_HWRENA
/* load the guest context from VCPU and return */
LONG_L $0, VCPU_R0(k1)
LONG_L $1, VCPU_R1(k1)
LONG_L $2, VCPU_R2(k1)
LONG_L $3, VCPU_R3(k1)
LONG_L $4, VCPU_R4(k1)
LONG_L $5, VCPU_R5(k1)
LONG_L $6, VCPU_R6(k1)
LONG_L $7, VCPU_R7(k1)
LONG_L $8, VCPU_R8(k1)
LONG_L $9, VCPU_R9(k1)
LONG_L $10, VCPU_R10(k1)
LONG_L $11, VCPU_R11(k1)
LONG_L $12, VCPU_R12(k1)
LONG_L $13, VCPU_R13(k1)
LONG_L $14, VCPU_R14(k1)
LONG_L $15, VCPU_R15(k1)
LONG_L $16, VCPU_R16(k1)
LONG_L $17, VCPU_R17(k1)
LONG_L $18, VCPU_R18(k1)
LONG_L $19, VCPU_R19(k1)
LONG_L $20, VCPU_R20(k1)
LONG_L $21, VCPU_R21(k1)
LONG_L $22, VCPU_R22(k1)
LONG_L $23, VCPU_R23(k1)
LONG_L $24, VCPU_R24(k1)
LONG_L $25, VCPU_R25(k1)
/* $/k1 loaded later */
LONG_L $28, VCPU_R28(k1)
LONG_L $29, VCPU_R29(k1)
LONG_L $30, VCPU_R30(k1)
LONG_L $31, VCPU_R31(k1)
FEXPORT(__kvm_mips_skip_guest_restore)
LONG_L k0, VCPU_HI(k1)
mthi k0
LONG_L k0, VCPU_LO(k1)
mtlo k0
LONG_L k0, VCPU_R26(k1)
LONG_L k1, VCPU_R27(k1)
eret
__kvm_mips_return_to_host:
/* EBASE is already pointing to Linux */
LONG_L k1, VCPU_HOST_STACK(k1)
INT_ADDIU k1,k1, -PT_SIZE
/* Restore host DDATA_LO */
LONG_L k0, PT_HOST_USERLOCAL(k1)
mtc0 k0, CP0_DDATA_LO
/* Restore host ASID */
LONG_L k0, PT_HOST_ASID(sp)
andi k0, 0xff
mtc0 k0,CP0_ENTRYHI
ehb
/* Load context saved on the host stack */
LONG_L $0, PT_R0(k1)
LONG_L $1, PT_R1(k1)
/*
* r2/v0 is the return code, shift it down by 2 (arithmetic)
* to recover the err code
*/
INT_SRA k0, v0, 2
move $2, k0
LONG_L $3, PT_R3(k1)
LONG_L $4, PT_R4(k1)
LONG_L $5, PT_R5(k1)
LONG_L $6, PT_R6(k1)
LONG_L $7, PT_R7(k1)
LONG_L $8, PT_R8(k1)
LONG_L $9, PT_R9(k1)
LONG_L $10, PT_R10(k1)
LONG_L $11, PT_R11(k1)
LONG_L $12, PT_R12(k1)
LONG_L $13, PT_R13(k1)
LONG_L $14, PT_R14(k1)
LONG_L $15, PT_R15(k1)
LONG_L $16, PT_R16(k1)
LONG_L $17, PT_R17(k1)
LONG_L $18, PT_R18(k1)
LONG_L $19, PT_R19(k1)
LONG_L $20, PT_R20(k1)
LONG_L $21, PT_R21(k1)
LONG_L $22, PT_R22(k1)
LONG_L $23, PT_R23(k1)
LONG_L $24, PT_R24(k1)
LONG_L $25, PT_R25(k1)
/* Host k0/k1 were not saved */
LONG_L $28, PT_R28(k1)
LONG_L $29, PT_R29(k1)
LONG_L $30, PT_R30(k1)
LONG_L k0, PT_HI(k1)
mthi k0
LONG_L k0, PT_LO(k1)
mtlo k0
/* Restore RDHWR access */
PTR_LI k0, 0x2000000F
mtc0 k0, CP0_HWRENA
/* Restore RA, which is the address we will return to */
LONG_L ra, PT_R31(k1)
j ra
nop
VECTOR_END(MIPSX(GuestExceptionEnd))
.end MIPSX(GuestException)
MIPSX(exceptions):
####
##### The exception handlers.
#####
.word _C_LABEL(MIPSX(GuestException)) # 0
.word _C_LABEL(MIPSX(GuestException)) # 1
.word _C_LABEL(MIPSX(GuestException)) # 2
.word _C_LABEL(MIPSX(GuestException)) # 3
.word _C_LABEL(MIPSX(GuestException)) # 4
.word _C_LABEL(MIPSX(GuestException)) # 5
.word _C_LABEL(MIPSX(GuestException)) # 6
.word _C_LABEL(MIPSX(GuestException)) # 7
.word _C_LABEL(MIPSX(GuestException)) # 8
.word _C_LABEL(MIPSX(GuestException)) # 9
.word _C_LABEL(MIPSX(GuestException)) # 10
.word _C_LABEL(MIPSX(GuestException)) # 11
.word _C_LABEL(MIPSX(GuestException)) # 12
.word _C_LABEL(MIPSX(GuestException)) # 13
.word _C_LABEL(MIPSX(GuestException)) # 14
.word _C_LABEL(MIPSX(GuestException)) # 15
.word _C_LABEL(MIPSX(GuestException)) # 16
.word _C_LABEL(MIPSX(GuestException)) # 17
.word _C_LABEL(MIPSX(GuestException)) # 18
.word _C_LABEL(MIPSX(GuestException)) # 19
.word _C_LABEL(MIPSX(GuestException)) # 20
.word _C_LABEL(MIPSX(GuestException)) # 21
.word _C_LABEL(MIPSX(GuestException)) # 22
.word _C_LABEL(MIPSX(GuestException)) # 23
.word _C_LABEL(MIPSX(GuestException)) # 24
.word _C_LABEL(MIPSX(GuestException)) # 25
.word _C_LABEL(MIPSX(GuestException)) # 26
.word _C_LABEL(MIPSX(GuestException)) # 27
.word _C_LABEL(MIPSX(GuestException)) # 28
.word _C_LABEL(MIPSX(GuestException)) # 29
.word _C_LABEL(MIPSX(GuestException)) # 30
.word _C_LABEL(MIPSX(GuestException)) # 31
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