It is possible to utilize 32-bit address encodings in virtual-8086 mode via an address override instruction prefix. However, the range of address is still limited to [0x-0xffff]. In such a case, return error.
Also, linear addresses in virtual-8086 mode are limited to 20 bits. Enforce such limit by truncating the most significant bytes of the computed linear address. Cc: Dave Hansen <[email protected]> Cc: Adam Buchbinder <[email protected]> Cc: Colin Ian King <[email protected]> Cc: Lorenzo Stoakes <[email protected]> Cc: Qiaowei Ren <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Masami Hiramatsu <[email protected]> Cc: Adrian Hunter <[email protected]> Cc: Kees Cook <[email protected]> Cc: Thomas Garnier <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Dmitry Vyukov <[email protected]> Cc: Ravi V. Shankar <[email protected]> Cc: [email protected] Signed-off-by: Ricardo Neri <[email protected]> --- arch/x86/lib/insn-eval.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index c7c1239..9822061 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -848,6 +848,12 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) linear_addr &= 0xffffffff; /* + * Even though 32-bit address encodings are allowed in virtual-8086 + * mode, the address range is still limited to [0x-0xffff]. + */ + if (v8086_mode(regs) && (linear_addr & ~0xffff)) + goto out_err; + /* * Make sure the effective address is within the limits of the * segment. In long mode, the limit is -1L. Thus, the second part * of the check always succeeds. @@ -857,6 +863,10 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) linear_addr += seg_base_addr; + /* Limit linear address to 20 bits */ + if (v8086_mode(regs)) + linear_addr &= 0xfffff; + return (void __user *)linear_addr; out_err: return (void __user *)-1; -- 2.9.3
