xref: /linux/arch/s390/kernel/alternative.c (revision bb9ae1a66c85eeb626864efd812c62026e126ec0)
1 // SPDX-License-Identifier: GPL-2.0
2 
3 #include <linux/uaccess.h>
4 #include <asm/nospec-branch.h>
5 #include <asm/abs_lowcore.h>
6 #include <asm/alternative.h>
7 #include <asm/facility.h>
8 
9 void __apply_alternatives(struct alt_instr *start, struct alt_instr *end, unsigned int ctx)
10 {
11 	u8 *instr, *replacement;
12 	struct alt_instr *a;
13 	bool replace;
14 
15 	/*
16 	 * The scan order should be from start to end. A later scanned
17 	 * alternative code can overwrite previously scanned alternative code.
18 	 */
19 	for (a = start; a < end; a++) {
20 		if (!(a->ctx & ctx))
21 			continue;
22 		switch (a->type) {
23 		case ALT_TYPE_FACILITY:
24 			replace = test_facility(a->data);
25 			break;
26 		case ALT_TYPE_SPEC:
27 			replace = nobp_enabled();
28 			break;
29 		case ALT_TYPE_LOWCORE:
30 			replace = have_relocated_lowcore();
31 			break;
32 		default:
33 			replace = false;
34 		}
35 		if (!replace)
36 			continue;
37 		instr = (u8 *)&a->instr_offset + a->instr_offset;
38 		replacement = (u8 *)&a->repl_offset + a->repl_offset;
39 		s390_kernel_write(instr, replacement, a->instrlen);
40 	}
41 }
42