insn_get_addr_ref() returns the effective address as defined by the section 3.7.5.1 Vol 1 of the Intel 64 and IA-32 Architectures Software Developer's Manual. In order to compute the linear address, we must add to the effective address the segment base address as set in the segment descriptor. Furthermore, the segment descriptor to use depends on the register that is used as the base of the effective address. The effective base address varies depending on whether the operand is a register or a memory address and on whether a SiB byte is used.
In most cases, the segment base address will be 0 if the USER_DS/USER32_DS segment is used or if segmentation is not used. However, the base address is not necessarily zero if a user programs defines its own segments. This is possible by using a local descriptor table.
Since the effective address is a signed quantity, the unsigned segment base address is saved in a separate variable and added to the final effective address.
Before returning the linear address, we check if the computed effective address is within the segment limit. In protected mode segment limits are not enforced. We can keep the check as get_seg_limit() return -1L in this case.
Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Adam Buchbinder adam.buchbinder@gmail.com Cc: Colin Ian King colin.king@canonical.com Cc: Lorenzo Stoakes lstoakes@gmail.com Cc: Qiaowei Ren qiaowei.ren@intel.com Cc: Arnaldo Carvalho de Melo acme@redhat.com Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Adrian Hunter adrian.hunter@intel.com Cc: Kees Cook keescook@chromium.org Cc: Thomas Garnier thgarnie@google.com Cc: Peter Zijlstra peterz@infradead.org Cc: Borislav Petkov bp@suse.de Cc: Dmitry Vyukov dvyukov@google.com Cc: Ravi V. Shankar ravi.v.shankar@intel.com Cc: x86@kernel.org Signed-off-by: Ricardo Neri ricardo.neri-calderon@linux.intel.com --- arch/x86/lib/insn-eval.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 4f600de..1a5f5a6 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -695,7 +695,7 @@ int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs) */ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) { - unsigned long linear_addr; + unsigned long linear_addr, seg_base_addr, seg_limit; long eff_addr, base, indx; int addr_offset, base_offset, indx_offset; insn_byte_t sib; @@ -709,6 +709,10 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) if (addr_offset < 0) goto out_err; eff_addr = regs_get_register(regs, addr_offset); + seg_base_addr = insn_get_seg_base(regs, insn, addr_offset); + if (seg_base_addr == -1L) + goto out_err; + seg_limit = get_seg_limit(regs, insn, addr_offset); } else { if (insn->sib.nbytes) { /* @@ -734,6 +738,11 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) indx = regs_get_register(regs, indx_offset);
eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); + seg_base_addr = insn_get_seg_base(regs, insn, + base_offset); + if (seg_base_addr == -1L) + goto out_err; + seg_limit = get_seg_limit(regs, insn, base_offset); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); /* @@ -751,10 +760,25 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) } else { eff_addr = regs_get_register(regs, addr_offset); } + seg_base_addr = insn_get_seg_base(regs, insn, + addr_offset); + if (seg_base_addr == -1L) + goto out_err; + seg_limit = get_seg_limit(regs, insn, addr_offset); } eff_addr += insn->displacement.value; } + linear_addr = (unsigned long)eff_addr; + /* + * 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. + */ + if (linear_addr > seg_limit) + goto out_err; + + linear_addr += seg_base_addr;
return (void __user *)linear_addr; out_err: