On Wed, 24 Mar 2021 15:48:34 +0000 Colin Ian King <[email protected]> wrote:
> Hi, > > Static analysis on linux-next using Coverity has detected an issue in > the following commit: > > commit 6256e668b7af9d81472e03c6a171630c08f8858a > Author: Masami Hiramatsu <[email protected]> > Date: Wed Mar 3 00:25:46 2021 +0900 > > x86/kprobes: Use int3 instead of debug trap for single-step > > The analysis is as follows: > > 160 switch (opcode & 0xf0) { > 161 case 0x60: > 162 /* can't boost "bound" */ > 163 return (opcode != 0x62); > 164 case 0x70: > 165 return 0; /* can't boost conditional jump */ > 166 case 0x90: > 167 return opcode != 0x9a; /* can't boost call far */ > 168 case 0xc0: > 169 /* can't boost software-interruptions */ > 170 return (0xc1 < opcode && opcode < 0xcc) || opcode == > 0xcf; > 171 case 0xd0: > 172 /* can boost AA* and XLAT */ > 173 return (opcode == 0xd4 || opcode == 0xd5 || opcode == > 0xd7); > 174 case 0xe0: > 175 /* can boost in/out and absolute jmps */ > 176 return ((opcode & 0x04) || opcode == 0xea); > 177 case 0xf0: > 178 /* clear and set flags are boostable */ > 179 return (opcode == 0xf5 || (0xf7 < opcode && opcode < > 0xfe)); > > dead_error_condition: The switch governing value opcode & 0xf0 cannot > be 255. > undefined (#1 of 1): Logically dead code (DEADCODE) > dead_error_begin: Execution cannot reach this statement: case 255: > > 180 case 0xff: > 181 /* indirect jmp is boostable */ > 182 return X86_MODRM_REG(insn->modrm.bytes[0]) == 4; > > the case 0xff statement can never be reached because the switch > statement is acting on opcode & 0xf0. Good catch! It must be under the case 0xf0... Thank you! -- Masami Hiramatsu <[email protected]>
