156 lines
5.9 KiB
Diff
156 lines
5.9 KiB
Diff
x86emul: enforce privilege level restrictions when loading CS
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Privilege level checks were basically missing for the CS case, the
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only check that was done (RPL == DPL for nonconforming segments)
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was solely covering a single special case (return to non-conforming
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segment).
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Additionally in long mode the L bit set requires the D bit to be clear,
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as was recently pointed out for KVM by Nadav Amit
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<namit@cs.technion.ac.il>.
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Finally we also need to force the loaded selector's RPL to CPL (at
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least as long as lret/retf emulation doesn't support privilege level
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changes).
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This is XSA-110.
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Signed-off-by: Jan Beulich <jbeulich@suse.com>
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Reviewed-by: Tim Deegan <tim@xen.org>
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--- xen/arch/x86/x86_emulate/x86_emulate.c
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+++ xen/arch/x86/x86_emulate/x86_emulate.c
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@@ -1119,7 +1119,7 @@ realmode_load_seg(
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static int
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protmode_load_seg(
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enum x86_segment seg,
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- uint16_t sel,
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+ uint16_t sel, bool_t is_ret,
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struct x86_emulate_ctxt *ctxt,
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const struct x86_emulate_ops *ops)
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{
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@@ -1185,9 +1185,23 @@ protmode_load_seg(
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/* Code segment? */
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if ( !(desc.b & (1u<<11)) )
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goto raise_exn;
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- /* Non-conforming segment: check DPL against RPL. */
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- if ( ((desc.b & (6u<<9)) != (6u<<9)) && (dpl != rpl) )
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+ if ( is_ret
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+ ? /*
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+ * Really rpl < cpl, but our sole caller doesn't handle
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+ * privilege level changes.
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+ */
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+ rpl != cpl || (desc.b & (1 << 10) ? dpl > rpl : dpl != rpl)
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+ : desc.b & (1 << 10)
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+ /* Conforming segment: check DPL against CPL. */
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+ ? dpl > cpl
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+ /* Non-conforming segment: check RPL and DPL against CPL. */
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+ : rpl > cpl || dpl != cpl )
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goto raise_exn;
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+ /* 64-bit code segments (L bit set) must have D bit clear. */
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+ if ( in_longmode(ctxt, ops) &&
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+ (desc.b & (1 << 21)) && (desc.b & (1 << 22)) )
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+ goto raise_exn;
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+ sel = (sel ^ rpl) | cpl;
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break;
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case x86_seg_ss:
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/* Writable data segment? */
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@@ -1252,7 +1266,7 @@ protmode_load_seg(
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static int
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load_seg(
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enum x86_segment seg,
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- uint16_t sel,
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+ uint16_t sel, bool_t is_ret,
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struct x86_emulate_ctxt *ctxt,
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const struct x86_emulate_ops *ops)
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{
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@@ -1261,7 +1275,7 @@ load_seg(
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return X86EMUL_UNHANDLEABLE;
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if ( in_protmode(ctxt, ops) )
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- return protmode_load_seg(seg, sel, ctxt, ops);
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+ return protmode_load_seg(seg, sel, is_ret, ctxt, ops);
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return realmode_load_seg(seg, sel, ctxt, ops);
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}
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@@ -2003,7 +2017,7 @@ x86_emulate(
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if ( (rc = read_ulong(x86_seg_ss, sp_post_inc(op_bytes),
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&dst.val, op_bytes, ctxt, ops)) != 0 )
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goto done;
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- if ( (rc = load_seg(src.val, (uint16_t)dst.val, ctxt, ops)) != 0 )
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+ if ( (rc = load_seg(src.val, dst.val, 0, ctxt, ops)) != 0 )
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return rc;
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break;
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@@ -2357,7 +2371,7 @@ x86_emulate(
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enum x86_segment seg = decode_segment(modrm_reg);
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generate_exception_if(seg == decode_segment_failed, EXC_UD, -1);
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generate_exception_if(seg == x86_seg_cs, EXC_UD, -1);
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- if ( (rc = load_seg(seg, (uint16_t)src.val, ctxt, ops)) != 0 )
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+ if ( (rc = load_seg(seg, src.val, 0, ctxt, ops)) != 0 )
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goto done;
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if ( seg == x86_seg_ss )
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ctxt->retire.flags.mov_ss = 1;
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@@ -2438,7 +2452,7 @@ x86_emulate(
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&_regs.eip, op_bytes, ctxt)) )
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goto done;
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- if ( (rc = load_seg(x86_seg_cs, sel, ctxt, ops)) != 0 )
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+ if ( (rc = load_seg(x86_seg_cs, sel, 0, ctxt, ops)) != 0 )
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goto done;
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_regs.eip = eip;
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break;
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@@ -2662,7 +2676,7 @@ x86_emulate(
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if ( (rc = read_ulong(src.mem.seg, src.mem.off + src.bytes,
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&sel, 2, ctxt, ops)) != 0 )
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goto done;
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- if ( (rc = load_seg(dst.val, (uint16_t)sel, ctxt, ops)) != 0 )
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+ if ( (rc = load_seg(dst.val, sel, 0, ctxt, ops)) != 0 )
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goto done;
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dst.val = src.val;
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break;
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@@ -2736,7 +2750,7 @@ x86_emulate(
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&dst.val, op_bytes, ctxt, ops)) ||
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(rc = read_ulong(x86_seg_ss, sp_post_inc(op_bytes + offset),
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&src.val, op_bytes, ctxt, ops)) ||
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- (rc = load_seg(x86_seg_cs, (uint16_t)src.val, ctxt, ops)) )
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+ (rc = load_seg(x86_seg_cs, src.val, 1, ctxt, ops)) )
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goto done;
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_regs.eip = dst.val;
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break;
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@@ -2785,7 +2799,7 @@ x86_emulate(
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_regs.eflags &= mask;
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_regs.eflags |= (uint32_t)(eflags & ~mask) | 0x02;
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_regs.eip = eip;
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- if ( (rc = load_seg(x86_seg_cs, (uint16_t)cs, ctxt, ops)) != 0 )
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+ if ( (rc = load_seg(x86_seg_cs, cs, 1, ctxt, ops)) != 0 )
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goto done;
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break;
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}
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@@ -3415,7 +3429,7 @@ x86_emulate(
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generate_exception_if(mode_64bit(), EXC_UD, -1);
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eip = insn_fetch_bytes(op_bytes);
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sel = insn_fetch_type(uint16_t);
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- if ( (rc = load_seg(x86_seg_cs, sel, ctxt, ops)) != 0 )
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+ if ( (rc = load_seg(x86_seg_cs, sel, 0, ctxt, ops)) != 0 )
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goto done;
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_regs.eip = eip;
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break;
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@@ -3714,7 +3728,7 @@ x86_emulate(
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goto done;
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}
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- if ( (rc = load_seg(x86_seg_cs, sel, ctxt, ops)) != 0 )
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+ if ( (rc = load_seg(x86_seg_cs, sel, 0, ctxt, ops)) != 0 )
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goto done;
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_regs.eip = src.val;
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@@ -3781,7 +3795,7 @@ x86_emulate(
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generate_exception_if(!in_protmode(ctxt, ops), EXC_UD, -1);
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generate_exception_if(!mode_ring0(), EXC_GP, 0);
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if ( (rc = load_seg((modrm_reg & 1) ? x86_seg_tr : x86_seg_ldtr,
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- src.val, ctxt, ops)) != 0 )
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+ src.val, 0, ctxt, ops)) != 0 )
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goto done;
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break;
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