Commit 6e3133d9 authored by Fenghua Yu's avatar Fenghua Yu Committed by Borislav Petkov
Browse files

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: default avatarFenghua Yu <fenghua.yu@intel.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarTony Luck <tony.luck@intel.com>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220207230254.3342514-11-fenghua.yu@intel.com
parent 7c1ef591

tools/objtool/arch/x86/decode.c

+10 −1
Original line number Diff line number Diff line
@@ -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 */