Even though memory addresses are unsigned, the operands used to compute the effective address do have a sign. This is true for the ModRM.rm, SIB.base, SIB.index as well as the displacement bytes. Thus, signed variables shall be used when computing the effective address from these operands. Once the signed effective address has been computed, it is casted to an unsigned long to determine the linear address.
Variables are renamed to better reflect the type of address being computed. Cc: Borislav Petkov <[email protected]> Cc: Andy Lutomirski <[email protected]> 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: Peter Zijlstra <[email protected]> Cc: Nathan Howard <[email protected]> Cc: Adan Hawthorn <[email protected]> Cc: Joe Perches <[email protected]> Cc: Ravi V. Shankar <[email protected]> Cc: [email protected] Signed-off-by: Ricardo Neri <[email protected]> --- arch/x86/mm/mpx.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 1c34b76..ebdead8 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -138,7 +138,8 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, */ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) { - unsigned long addr, base, indx; + unsigned long linear_addr; + long eff_addr, base, indx; int addr_offset, base_offset, indx_offset; insn_byte_t sib; @@ -150,7 +151,7 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); if (addr_offset < 0) goto out_err; - addr = regs_get_register(regs, addr_offset); + eff_addr = regs_get_register(regs, addr_offset); } else { if (insn->sib.nbytes) { base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE); @@ -163,16 +164,18 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) base = regs_get_register(regs, base_offset); indx = regs_get_register(regs, indx_offset); - addr = base + indx * (1 << X86_SIB_SCALE(sib)); + eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); if (addr_offset < 0) goto out_err; - addr = regs_get_register(regs, addr_offset); + eff_addr = regs_get_register(regs, addr_offset); } - addr += insn->displacement.value; + eff_addr += insn->displacement.value; } - return (void __user *)addr; + linear_addr = (unsigned long)eff_addr; + + return (void __user *)linear_addr; out_err: return (void __user *)-1; } -- 2.9.3
