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 saved in a separate variable and added to the final effective address.
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 | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index ea10b03..edb360f 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -566,7 +566,7 @@ int insn_get_reg_offset_sib_index(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; long eff_addr, base, indx; int addr_offset, base_offset, indx_offset; insn_byte_t sib; @@ -580,6 +580,8 @@ 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, + false); } else { if (insn->sib.nbytes) { /* @@ -605,6 +607,8 @@ 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, false); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); /* -EDOM means that we must ignore the address_offset. @@ -623,10 +627,12 @@ 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, false); } eff_addr += insn->displacement.value; } - linear_addr = (unsigned long)eff_addr; + linear_addr = (unsigned long)eff_addr + seg_base_addr;
return (void __user *)linear_addr; out_err: