7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Lukas Zobernig [ Upstream commit 32c52ec87d6245ee2d12ed5dd509e40062939b50 ] Commit 45e1dccc0653 ("x86/insn: Simplify for_each_insn_prefix()") made for_each_insn_prefix() declare its own loop counter named idx. get_seg_reg_override_idx() keeps its result in a local of the same name, so the assignments in the loop body now write the loop counter: - the function always returns INAT_SEG_REG_DEFAULT, so FS and GS overrides are ignored; - a CS override sets the counter to INAT_SEG_REG_CS (2), the increment makes it 3, and prefixes.bytes[3] holds the last prefix, 0x2e again, so the loop never terminates. The UMIP emulation reaches this from the #GP handler for user space: an SGDT, SIDT or SMSW with a memory operand and a CS prefix leaves the task spinning in the kernel, never returning to user space, with a SIGKILL that is never delivered. Any user can thus tie up CPUs until reboot. With an FS or GS prefix, the emulated result is written to the wrong address. Rename the internal macro iterator variable. [ Lukas' original patch renamed the use site, I changed it to rename the iterator in the macro instead, but left Lukas' commit message and authorship - Linus ] Fixes: 45e1dccc0653 ("x86/insn: Simplify for_each_insn_prefix()") Signed-off-by: Lukas Zobernig Acked-by: Peter Zijlstra Acked-by: Borislav Petkov Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- arch/x86/include/asm/insn.h | 2 +- tools/arch/x86/include/asm/insn.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h index 846d21c1a7f88..8fb92da1a2c46 100644 --- a/arch/x86/include/asm/insn.h +++ b/arch/x86/include/asm/insn.h @@ -321,7 +321,7 @@ static inline int insn_offset_immediate(struct insn *insn) * are repeated, it cannot be used for looping over the prefixes. */ #define for_each_insn_prefix(insn, prefix) \ - for (int idx = 0; idx < ARRAY_SIZE(insn->prefixes.bytes) && (prefix = insn->prefixes.bytes[idx]) != 0; idx++) + for (int __i = 0; __i < ARRAY_SIZE(insn->prefixes.bytes) && (prefix = insn->prefixes.bytes[__i]) != 0; __i++) #define POP_SS_OPCODE 0x1f #define MOV_SREG_OPCODE 0x8e diff --git a/tools/arch/x86/include/asm/insn.h b/tools/arch/x86/include/asm/insn.h index 8f10f29433703..1d2903508bbeb 100644 --- a/tools/arch/x86/include/asm/insn.h +++ b/tools/arch/x86/include/asm/insn.h @@ -321,7 +321,7 @@ static inline int insn_offset_immediate(struct insn *insn) * are repeated, it cannot be used for looping over the prefixes. */ #define for_each_insn_prefix(insn, prefix) \ - for (int idx = 0; idx < ARRAY_SIZE(insn->prefixes.bytes) && (prefix = insn->prefixes.bytes[idx]) != 0; idx++) + for (int __i = 0; __i < ARRAY_SIZE(insn->prefixes.bytes) && (prefix = insn->prefixes.bytes[__i]) != 0; __i++) #define POP_SS_OPCODE 0x1f #define MOV_SREG_OPCODE 0x8e -- 2.53.0