The following commit has been merged into the x86/pasid branch of tip: Commit-ID: 6e3133d901e89a4ba83ce7ebd8c27bbeaa9ed1f2 Gitweb: https://git.kernel.org/tip/6e3133d901e89a4ba83ce7ebd8c27bbeaa9ed1f2 Author: Fenghua Yu <fenghua.yu@xxxxxxxxx> AuthorDate: Mon, 07 Feb 2022 15:02:53 -08:00 Committer: Borislav Petkov <bp@xxxxxxx> CommitterDate: Tue, 15 Feb 2022 11:31:43 +01:00 tools/objtool: Check for use of the ENQCMD instruction in the kernel The ENQCMD instruction implicitly accesses the PASID_MSR to fill in the pasid field of the descriptor being submitted to an accelerator. But there is no precise (and stable across kernel changes) point at which the PASID_MSR is updated from the value for one task to the next. Kernel code that uses accelerators must always use the ENQCMDS instruction which does not access the PASID_MSR. Check for use of the ENQCMD instruction in the kernel and warn on its usage. Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx> Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Link: https://lore.kernel.org/r/20220207230254.3342514-11-fenghua.yu@xxxxxxxxx --- tools/objtool/arch/x86/decode.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c index c10ef78..479e769 100644 --- a/tools/objtool/arch/x86/decode.c +++ b/tools/objtool/arch/x86/decode.c @@ -112,7 +112,7 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec const struct elf *elf = file->elf; struct insn insn; int x86_64, ret; - unsigned char op1, op2, + unsigned char op1, op2, op3, rex = 0, rex_b = 0, rex_r = 0, rex_w = 0, rex_x = 0, modrm = 0, modrm_mod = 0, modrm_rm = 0, modrm_reg = 0, sib = 0, /* sib_scale = 0, */ sib_index = 0, sib_base = 0; @@ -139,6 +139,7 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec op1 = insn.opcode.bytes[0]; op2 = insn.opcode.bytes[1]; + op3 = insn.opcode.bytes[2]; if (insn.rex_prefix.nbytes) { rex = insn.rex_prefix.bytes[0]; @@ -491,6 +492,14 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec /* nopl/nopw */ *type = INSN_NOP; + } else if (op2 == 0x38 && op3 == 0xf8) { + if (insn.prefixes.nbytes == 1 && + insn.prefixes.bytes[0] == 0xf2) { + /* ENQCMD cannot be used in the kernel. */ + WARN("ENQCMD instruction at %s:%lx", sec->name, + offset); + } + } else if (op2 == 0xa0 || op2 == 0xa8) { /* push fs/gs */
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