linux-kernel - [PATCH 5.10 005/100] s390/module: fix loading modules with a lot of relocations

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Date:   Mon, 31 Jan 2022 11:55:26 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andrea Righi <andrea.righi@...onical.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>
Subject: [PATCH 5.10 005/100] s390/module: fix loading modules with a lot of relocations

From: Ilya Leoshkevich <iii@...ux.ibm.com>

commit f3b7e73b2c6619884351a3a0a7468642f852b8a2 upstream.

If the size of the PLT entries generated by apply_rela() exceeds
64KiB, the first ones can no longer reach __jump_r1 with brc. Fix by
using brcl. An alternative solution is to add a __jump_r1 copy after
every 64KiB, however, the space savings are quite small and do not
justify the additional complexity.

Fixes: f19fbd5ed642 ("s390: introduce execute-trampolines for branches")
Cc: stable@...r.kernel.org
Reported-by: Andrea Righi <andrea.righi@...onical.com>
Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
Reviewed-by: Heiko Carstens <hca@...ux.ibm.com>
Cc: Vasily Gorbik <gor@...ux.ibm.com>
Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>
Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/s390/kernel/module.c |   37 ++++++++++++++++++-------------------
 1 file changed, 18 insertions(+), 19 deletions(-)

--- a/arch/s390/kernel/module.c
+++ b/arch/s390/kernel/module.c
@@ -30,7 +30,7 @@
 #define DEBUGP(fmt , ...)
 #endif
 
-#define PLT_ENTRY_SIZE 20
+#define PLT_ENTRY_SIZE 22
 
 void *module_alloc(unsigned long size)
 {
@@ -330,27 +330,26 @@ static int apply_rela(Elf_Rela *rela, El
 	case R_390_PLTOFF32:	/* 32 bit offset from GOT to PLT. */
 	case R_390_PLTOFF64:	/* 16 bit offset from GOT to PLT. */
 		if (info->plt_initialized == 0) {
-			unsigned int insn[5];
-			unsigned int *ip = me->core_layout.base +
-					   me->arch.plt_offset +
-					   info->plt_offset;
-
-			insn[0] = 0x0d10e310;	/* basr 1,0  */
-			insn[1] = 0x100a0004;	/* lg	1,10(1) */
+			unsigned char insn[PLT_ENTRY_SIZE];
+			char *plt_base;
+			char *ip;
+
+			plt_base = me->core_layout.base + me->arch.plt_offset;
+			ip = plt_base + info->plt_offset;
+			*(int *)insn = 0x0d10e310;	/* basr 1,0  */
+			*(int *)&insn[4] = 0x100c0004;	/* lg	1,12(1) */
 			if (IS_ENABLED(CONFIG_EXPOLINE) && !nospec_disable) {
-				unsigned int *ij;
-				ij = me->core_layout.base +
-					me->arch.plt_offset +
-					me->arch.plt_size - PLT_ENTRY_SIZE;
-				insn[2] = 0xa7f40000 +	/* j __jump_r1 */
-					(unsigned int)(u16)
-					(((unsigned long) ij - 8 -
-					  (unsigned long) ip) / 2);
+				char *jump_r1;
+
+				jump_r1 = plt_base + me->arch.plt_size -
+					PLT_ENTRY_SIZE;
+				/* brcl	0xf,__jump_r1 */
+				*(short *)&insn[8] = 0xc0f4;
+				*(int *)&insn[10] = (jump_r1 - (ip + 8)) / 2;
 			} else {
-				insn[2] = 0x07f10000;	/* br %r1 */
+				*(int *)&insn[8] = 0x07f10000;	/* br %r1 */
 			}
-			insn[3] = (unsigned int) (val >> 32);
-			insn[4] = (unsigned int) val;
+			*(long *)&insn[14] = val;
 
 			write(ip, insn, sizeof(insn));
 			info->plt_initialized = 1;