[PATCH v4 06/11] s390/module: Use s390_kernel_write() for late relocations

Josh Poimboeuf
2020-04-29T15:25:35Z

From: Peter Zijlstra <peterz@infradead.org>

Because of late module patching, a livepatch module needs to be able to
apply some of its relocations well after it has been loaded. Instead of
playing games with module_{dis,en}able_ro(), use existing text poking
mechanisms to apply relocations after module loading.

So far only x86, s390 and Power have HAVE_LIVEPATCH but only the first
two also have STRICT_MODULE_RWX.

This will allow removal of the last module_disable_ro() usage in
livepatch. The ultimate goal is to completely disallow making
executable mappings writable.

[ jpoimboe: Split up patches. Use mod state to determine whether
memcpy() can be used. Test and add fixes. ]

Cc: linux-s390@vger.kernel.org
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
arch/s390/kernel/module.c | 147 +++++++++++++++++++++++---------------
1 file changed, 88 insertions(+), 59 deletions(-)

diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c
index ba8f19bb438b..4055f1c49814 100644
--- a/arch/s390/kernel/module.c
+++ b/arch/s390/kernel/module.c
@@ -19,6 +19,7 @@
#include <linux/kasan.h>
#include <linux/moduleloader.h>
#include <linux/bug.h>
+#include <linux/memory.h>
#include <asm/alternative.h>
#include <asm/nospec-branch.h>
#include <asm/facility.h>
@@ -174,10 +175,12 @@ int module_frob_arch_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
}

static int apply_rela_bits(Elf_Addr loc, Elf_Addr val,
- int sign, int bits, int shift)
+ int sign, int bits, int shift,
+ void *(*write)(void *dest, const void *src, size_t len))
{
unsigned long umax;
long min, max;
+ void *dest = (void *)loc;

if (val & ((1UL << shift) - 1))
return -ENOEXEC;
@@ -194,26 +197,33 @@ static int apply_rela_bits(Elf_Addr loc, Elf_Addr val,
return -ENOEXEC;
}

- if (bits == 8)
- *(unsigned char *) loc = val;
- else if (bits == 12)
- *(unsigned short *) loc = (val & 0xfff) |
+ if (bits == 8) {
+ unsigned char tmp = val;
+ write(dest, &tmp, 1);
+ } else if (bits == 12) {
+ unsigned short tmp = (val & 0xfff) |
(*(unsigned short *) loc & 0xf000);
- else if (bits == 16)
- *(unsigned short *) loc = val;
- else if (bits == 20)
- *(unsigned int *) loc = (val & 0xfff) << 16 |
- (val & 0xff000) >> 4 |
- (*(unsigned int *) loc & 0xf00000ff);
- else if (bits == 32)
- *(unsigned int *) loc = val;
- else if (bits == 64)
- *(unsigned long *) loc = val;
+ write(dest, &tmp, 2);
+ } else if (bits == 16) {
+ unsigned short tmp = val;
+ write(dest, &tmp, 2);
+ } else if (bits == 20) {
+ unsigned int tmp = (val & 0xfff) << 16 |
+ (val & 0xff000) >> 4 | (*(unsigned int *) loc & 0xf00000ff);
+ write(dest, &tmp, 4);
+ } else if (bits == 32) {
+ unsigned int tmp = val;
+ write(dest, &tmp, 4);
+ } else if (bits == 64) {
+ unsigned long tmp = val;
+ write(dest, &tmp, 8);
+ }
return 0;
}

static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
- const char *strtab, struct module *me)
+ const char *strtab, struct module *me,
+ void *(*write)(void *dest, const void *src, size_t len))
{
struct mod_arch_syminfo *info;
Elf_Addr loc, val;
@@ -241,17 +251,17 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
case R_390_64: /* Direct 64 bit. */
val += rela->r_addend;
if (r_type == R_390_8)
- rc = apply_rela_bits(loc, val, 0, 8, 0);
+ rc = apply_rela_bits(loc, val, 0, 8, 0, write);
else if (r_type == R_390_12)
- rc = apply_rela_bits(loc, val, 0, 12, 0);
+ rc = apply_rela_bits(loc, val, 0, 12, 0, write);
else if (r_type == R_390_16)
- rc = apply_rela_bits(loc, val, 0, 16, 0);
+ rc = apply_rela_bits(loc, val, 0, 16, 0, write);
else if (r_type == R_390_20)
- rc = apply_rela_bits(loc, val, 1, 20, 0);
+ rc = apply_rela_bits(loc, val, 1, 20, 0, write);
else if (r_type == R_390_32)
- rc = apply_rela_bits(loc, val, 0, 32, 0);
+ rc = apply_rela_bits(loc, val, 0, 32, 0, write);
else if (r_type == R_390_64)
- rc = apply_rela_bits(loc, val, 0, 64, 0);
+ rc = apply_rela_bits(loc, val, 0, 64, 0, write);
break;
case R_390_PC16: /* PC relative 16 bit. */
case R_390_PC16DBL: /* PC relative 16 bit shifted by 1. */
@@ -260,15 +270,15 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
case R_390_PC64: /* PC relative 64 bit. */
val += rela->r_addend - loc;
if (r_type == R_390_PC16)
- rc = apply_rela_bits(loc, val, 1, 16, 0);
+ rc = apply_rela_bits(loc, val, 1, 16, 0, write);
else if (r_type == R_390_PC16DBL)
- rc = apply_rela_bits(loc, val, 1, 16, 1);
+ rc = apply_rela_bits(loc, val, 1, 16, 1, write);
else if (r_type == R_390_PC32DBL)
- rc = apply_rela_bits(loc, val, 1, 32, 1);
+ rc = apply_rela_bits(loc, val, 1, 32, 1, write);
else if (r_type == R_390_PC32)
- rc = apply_rela_bits(loc, val, 1, 32, 0);
+ rc = apply_rela_bits(loc, val, 1, 32, 0, write);
else if (r_type == R_390_PC64)
- rc = apply_rela_bits(loc, val, 1, 64, 0);
+ rc = apply_rela_bits(loc, val, 1, 64, 0, write);
break;
case R_390_GOT12: /* 12 bit GOT offset. */
case R_390_GOT16: /* 16 bit GOT offset. */
@@ -283,33 +293,33 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
case R_390_GOTPLT64: /* 64 bit offset to jump slot. */
case R_390_GOTPLTENT: /* 32 bit rel. offset to jump slot >> 1. */
if (info->got_initialized == 0) {
- Elf_Addr *gotent;
+ Elf_Addr *gotent = me->core_layout.base +
+ me->arch.got_offset +
+ info->got_offset;

- gotent = me->core_layout.base + me->arch.got_offset +
- info->got_offset;
- *gotent = val;
+ write(gotent, &val, sizeof(*gotent));
info->got_initialized = 1;
}
val = info->got_offset + rela->r_addend;
if (r_type == R_390_GOT12 ||
r_type == R_390_GOTPLT12)
- rc = apply_rela_bits(loc, val, 0, 12, 0);
+ rc = apply_rela_bits(loc, val, 0, 12, 0, write);
else if (r_type == R_390_GOT16 ||
r_type == R_390_GOTPLT16)
- rc = apply_rela_bits(loc, val, 0, 16, 0);
+ rc = apply_rela_bits(loc, val, 0, 16, 0, write);
else if (r_type == R_390_GOT20 ||
r_type == R_390_GOTPLT20)
- rc = apply_rela_bits(loc, val, 1, 20, 0);
+ rc = apply_rela_bits(loc, val, 1, 20, 0, write);
else if (r_type == R_390_GOT32 ||
r_type == R_390_GOTPLT32)
- rc = apply_rela_bits(loc, val, 0, 32, 0);
+ rc = apply_rela_bits(loc, val, 0, 32, 0, write);
else if (r_type == R_390_GOT64 ||
r_type == R_390_GOTPLT64)
- rc = apply_rela_bits(loc, val, 0, 64, 0);
+ rc = apply_rela_bits(loc, val, 0, 64, 0, write);
else if (r_type == R_390_GOTENT ||
r_type == R_390_GOTPLTENT) {
val += (Elf_Addr) me->core_layout.base - loc;
- rc = apply_rela_bits(loc, val, 1, 32, 1);
+ rc = apply_rela_bits(loc, val, 1, 32, 1, write);
}
break;
case R_390_PLT16DBL: /* 16 bit PC rel. PLT shifted by 1. */
@@ -320,25 +330,29 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
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 *ip;
- ip = me->core_layout.base + me->arch.plt_offset +
- info->plt_offset;
- ip[0] = 0x0d10e310; /* basr 1,0 */
- ip[1] = 0x100a0004; /* lg 1,10(1) */
+ 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) */
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;
- ip[2] = 0xa7f40000 + /* j __jump_r1 */
+ insn[2] = 0xa7f40000 + /* j __jump_r1 */
(unsigned int)(u16)
(((unsigned long) ij - 8 -
(unsigned long) ip) / 2);
} else {
- ip[2] = 0x07f10000; /* br %r1 */
+ insn[2] = 0x07f10000; /* br %r1 */
}
- ip[3] = (unsigned int) (val >> 32);
- ip[4] = (unsigned int) val;
+ insn[3] = (unsigned int) (val >> 32);
+ insn[4] = (unsigned int) val;
+
+ write(ip, insn, sizeof(insn));
info->plt_initialized = 1;
}
if (r_type == R_390_PLTOFF16 ||
@@ -357,17 +371,17 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
val += rela->r_addend - loc;
}
if (r_type == R_390_PLT16DBL)
- rc = apply_rela_bits(loc, val, 1, 16, 1);
+ rc = apply_rela_bits(loc, val, 1, 16, 1, write);
else if (r_type == R_390_PLTOFF16)
- rc = apply_rela_bits(loc, val, 0, 16, 0);
+ rc = apply_rela_bits(loc, val, 0, 16, 0, write);
else if (r_type == R_390_PLT32DBL)
- rc = apply_rela_bits(loc, val, 1, 32, 1);
+ rc = apply_rela_bits(loc, val, 1, 32, 1, write);
else if (r_type == R_390_PLT32 ||
r_type == R_390_PLTOFF32)
- rc = apply_rela_bits(loc, val, 0, 32, 0);
+ rc = apply_rela_bits(loc, val, 0, 32, 0, write);
else if (r_type == R_390_PLT64 ||
r_type == R_390_PLTOFF64)
- rc = apply_rela_bits(loc, val, 0, 64, 0);
+ rc = apply_rela_bits(loc, val, 0, 64, 0, write);
break;
case R_390_GOTOFF16: /* 16 bit offset to GOT. */
case R_390_GOTOFF32: /* 32 bit offset to GOT. */
@@ -375,20 +389,20 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
val = val + rela->r_addend -
((Elf_Addr) me->core_layout.base + me->arch.got_offset);
if (r_type == R_390_GOTOFF16)
- rc = apply_rela_bits(loc, val, 0, 16, 0);
+ rc = apply_rela_bits(loc, val, 0, 16, 0, write);
else if (r_type == R_390_GOTOFF32)
- rc = apply_rela_bits(loc, val, 0, 32, 0);
+ rc = apply_rela_bits(loc, val, 0, 32, 0, write);
else if (r_type == R_390_GOTOFF64)
- rc = apply_rela_bits(loc, val, 0, 64, 0);
+ rc = apply_rela_bits(loc, val, 0, 64, 0, write);
break;
case R_390_GOTPC: /* 32 bit PC relative offset to GOT. */
case R_390_GOTPCDBL: /* 32 bit PC rel. off. to GOT shifted by 1. */
val = (Elf_Addr) me->core_layout.base + me->arch.got_offset +
rela->r_addend - loc;
if (r_type == R_390_GOTPC)
- rc = apply_rela_bits(loc, val, 1, 32, 0);
+ rc = apply_rela_bits(loc, val, 1, 32, 0, write);
else if (r_type == R_390_GOTPCDBL)
- rc = apply_rela_bits(loc, val, 1, 32, 1);
+ rc = apply_rela_bits(loc, val, 1, 32, 1, write);
break;
case R_390_COPY:
case R_390_GLOB_DAT: /* Create GOT entry. */
@@ -412,9 +426,10 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
return 0;
}

-int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
+static int __apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
unsigned int symindex, unsigned int relsec,
- struct module *me)
+ struct module *me,
+ void *(*write)(void *dest, const void *src, size_t len))
{
Elf_Addr base;
Elf_Sym *symtab;
@@ -430,13 +445,27 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
n = sechdrs[relsec].sh_size / sizeof(Elf_Rela);

for (i = 0; i < n; i++, rela++) {
- rc = apply_rela(rela, base, symtab, strtab, me);
+ rc = apply_rela(rela, base, symtab, strtab, me, write);
if (rc)
return rc;
}
return 0;
}

+int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
+ unsigned int symindex, unsigned int relsec,
+ struct module *me)
+{
+ bool early = me->state == MODULE_STATE_UNFORMED;
+ void *(*write)(void *, const void *, size_t) = memcpy;
+
+ if (!early)
+ write = s390_kernel_write;
+
+ return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
+ write);
+}
+
int module_finalize(const Elf_Ehdr *hdr,
const Elf_Shdr *sechdrs,
struct module *me)
--
2.21.1