xref: /openbmc/linux/arch/s390/purgatory/head.S (revision cada938a)
1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Purgatory setup code
4 *
5 * Copyright IBM Corp. 2018
6 *
7 * Author(s): Philipp Rudo <prudo@linux.vnet.ibm.com>
8 */
9
10#include <linux/linkage.h>
11#include <asm/asm-offsets.h>
12#include <asm/page.h>
13#include <asm/sigp.h>
14#include <asm/ptrace.h>
15
16/* The purgatory is the code running between two kernels. It's main purpose
17 * is to verify that the next kernel was not corrupted after load and to
18 * start it.
19 *
20 * If the next kernel is a crash kernel there are some peculiarities to
21 * consider:
22 *
23 * First the purgatory is called twice. Once only to verify the
24 * sha digest. So if the crash kernel got corrupted the old kernel can try
25 * to trigger a stand-alone dumper. And once to actually load the crash kernel.
26 *
27 * Second the purgatory also has to swap the crash memory region with its
28 * destination at address 0. As the purgatory is part of crash memory this
29 * requires some finesse. The tactic here is that the purgatory first copies
30 * itself to the end of the destination and then swaps the rest of the
31 * memory running from there.
32 */
33
34#define bufsz purgatory_end-stack
35
36.macro MEMCPY dst,src,len
37	lgr	%r0,\dst
38	lgr	%r1,\len
39	lgr	%r2,\src
40	lgr	%r3,\len
41
4220:	mvcle	%r0,%r2,0
43	jo	20b
44.endm
45
46.macro MEMSWAP dst,src,buf,len
4710:	larl	%r0,purgatory_end
48	larl	%r1,stack
49	slgr	%r0,%r1
50	cgr	\len,%r0
51	jh	11f
52	lgr	%r4,\len
53	j	12f
5411:	lgr	%r4,%r0
55
5612:	MEMCPY	\buf,\dst,%r4
57	MEMCPY	\dst,\src,%r4
58	MEMCPY	\src,\buf,%r4
59
60	agr	\dst,%r4
61	agr	\src,%r4
62	sgr	\len,%r4
63
64	cghi	\len,0
65	jh	10b
66.endm
67
68.macro START_NEXT_KERNEL base subcode
69	lg	%r4,kernel_entry-\base(%r13)
70	lg	%r5,load_psw_mask-\base(%r13)
71	ogr	%r4,%r5
72	stg	%r4,0(%r0)
73
74	xgr	%r0,%r0
75	lghi	%r1,\subcode
76	diag	%r0,%r1,0x308
77.endm
78
79	.text
80	.balign PAGE_SIZE
81SYM_CODE_START(purgatory_start)
82	/* The purgatory might be called after a diag308 so better set
83	 * architecture and addressing mode.
84	 */
85	lhi	%r1,1
86	sigp	%r1,%r0,SIGP_SET_ARCHITECTURE
87	sam64
88
89	larl	%r5,gprregs
90	stmg	%r6,%r15,0(%r5)
91
92	basr	%r13,0
93.base_crash:
94
95	/* Setup stack */
96	larl	%r15,purgatory_end-STACK_FRAME_OVERHEAD
97
98	/* If the next kernel is KEXEC_TYPE_CRASH the purgatory is called
99	 * directly with a flag passed in %r2 whether the purgatory shall do
100	 * checksum verification only (%r2 = 0 -> verification only).
101	 *
102	 * Check now and preserve over C function call by storing in
103	 * %r10 with
104	 *	1 -> checksum verification only
105	 *	0 -> load new kernel
106	 */
107	lghi	%r10,0
108	lg	%r11,kernel_type-.base_crash(%r13)
109	cghi	%r11,1		/* KEXEC_TYPE_CRASH */
110	jne	.do_checksum_verification
111	cghi	%r2,0		/* checksum verification only */
112	jne	.do_checksum_verification
113	lghi	%r10,1
114
115.do_checksum_verification:
116	brasl	%r14,verify_sha256_digest
117
118	cghi	%r10,1		/* checksum verification only */
119	je	.return_old_kernel
120	cghi	%r2,0		/* checksum match */
121	jne	.disabled_wait
122
123	/* If the next kernel is a crash kernel the purgatory has to swap
124	 * the mem regions first.
125	 */
126	cghi	%r11,1 /* KEXEC_TYPE_CRASH */
127	je	.start_crash_kernel
128
129	/* start normal kernel */
130	START_NEXT_KERNEL .base_crash 0
131
132.return_old_kernel:
133	lmg	%r6,%r15,gprregs-.base_crash(%r13)
134	br	%r14
135
136.disabled_wait:
137	lpswe	disabled_wait_psw-.base_crash(%r13)
138
139.start_crash_kernel:
140	/* Location of purgatory_start in crash memory */
141	larl	%r0,.base_crash
142	larl	%r1,purgatory_start
143	slgr	%r0,%r1
144	lgr	%r8,%r13
145	sgr	%r8,%r0
146
147	/* Destination for this code i.e. end of memory to be swapped. */
148	larl	%r0,purgatory_end
149	larl	%r1,purgatory_start
150	slgr	%r0,%r1
151	lg	%r9,crash_size-.base_crash(%r13)
152	sgr	%r9,%r0
153
154	/* Destination in crash memory, i.e. same as r9 but in crash memory. */
155	lg	%r10,crash_start-.base_crash(%r13)
156	agr	%r10,%r9
157
158	/* Buffer location (in crash memory) and size. As the purgatory is
159	 * behind the point of no return it can re-use the stack as buffer.
160	 */
161	larl	%r11,purgatory_end
162	larl	%r12,stack
163	slgr	%r11,%r12
164
165	MEMCPY	%r12,%r9,%r11	/* dst	-> (crash) buf */
166	MEMCPY	%r9,%r8,%r11	/* self -> dst */
167
168	/* Jump to new location. */
169	lgr	%r7,%r9
170	larl	%r0,.jump_to_dst
171	larl	%r1,purgatory_start
172	slgr	%r0,%r1
173	agr	%r7,%r0
174	br	%r7
175
176.jump_to_dst:
177	basr	%r13,0
178.base_dst:
179
180	/* clear buffer */
181	MEMCPY	%r12,%r10,%r11	/* (crash) buf -> (crash) dst */
182
183	/* Load new buffer location after jump */
184	larl	%r7,stack
185	lgr	%r0,%r7
186	larl	%r1,purgatory_start
187	slgr	%r0,%r1
188	agr	%r10,%r0
189	MEMCPY	%r10,%r7,%r11	/* (new) buf -> (crash) buf */
190
191	/* Now the code is set up to run from its designated location. Start
192	 * swapping the rest of crash memory now.
193	 *
194	 * The registers will be used as follow:
195	 *
196	 *	%r0-%r4	reserved for macros defined above
197	 *	%r5-%r6 tmp registers
198	 *	%r7	pointer to current struct sha region
199	 *	%r8	index to iterate over all sha regions
200	 *	%r9	pointer in crash memory
201	 *	%r10	pointer in old kernel
202	 *	%r11	total size (still) to be moved
203	 *	%r12	pointer to buffer
204	 */
205	lgr	%r12,%r7
206	lgr	%r11,%r9
207	lghi	%r10,0
208	lg	%r9,crash_start-.base_dst(%r13)
209	lghi	%r8,16	/* KEXEC_SEGMENTS_MAX */
210	larl	%r7,purgatory_sha_regions
211
212	j .loop_first
213
214	/* Loop over all purgatory_sha_regions. */
215.loop_next:
216	aghi	%r8,-1
217	cghi	%r8,0
218	je	.loop_out
219
220	aghi	%r7,__KEXEC_SHA_REGION_SIZE
221
222.loop_first:
223	lg	%r5,__KEXEC_SHA_REGION_START(%r7)
224	cghi	%r5,0
225	je	.loop_next
226
227	/* Copy [end last sha region, start current sha region) */
228	/* Note: kexec_sha_region->start points in crash memory */
229	sgr	%r5,%r9
230	MEMCPY	%r9,%r10,%r5
231
232	agr	%r9,%r5
233	agr	%r10,%r5
234	sgr	%r11,%r5
235
236	/* Swap sha region */
237	lg	%r6,__KEXEC_SHA_REGION_LEN(%r7)
238	MEMSWAP	%r9,%r10,%r12,%r6
239	sg	%r11,__KEXEC_SHA_REGION_LEN(%r7)
240	j	.loop_next
241
242.loop_out:
243	/* Copy rest of crash memory */
244	MEMCPY	%r9,%r10,%r11
245
246	/* start crash kernel */
247	START_NEXT_KERNEL .base_dst 1
248SYM_CODE_END(purgatory_start)
249
250SYM_DATA_LOCAL(load_psw_mask,		.long 0x00080000,0x80000000)
251	.balign	8
252SYM_DATA_LOCAL(disabled_wait_psw,	.quad 0x0002000180000000,.do_checksum_verification)
253SYM_DATA_LOCAL(gprregs,			.fill 10,8,0)
254SYM_DATA(purgatory_sha256_digest,	.skip 32)
255SYM_DATA(purgatory_sha_regions,		.skip 16*__KEXEC_SHA_REGION_SIZE)
256SYM_DATA(kernel_entry,			.skip 8)
257SYM_DATA(kernel_type,			.skip 8)
258SYM_DATA(crash_start,			.skip 8)
259SYM_DATA(crash_size,			.skip 8)
260	.balign	PAGE_SIZE
261SYM_DATA_START_LOCAL(stack)
262	/* The buffer to move this code must be as big as the code. */
263	.skip	stack-purgatory_start
264	.balign	PAGE_SIZE
265SYM_DATA_END_LABEL(stack, SYM_L_LOCAL, purgatory_end)
266