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powerpc/module_32: Fix livepatching for RO modules

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Livepatching a loaded module involves applying relocations through
apply_relocate_add(), which attempts to write to read-only memory when
CONFIG_STRICT_MODULE_RWX=y.

R_PPC_ADDR16_LO, R_PPC_ADDR16_HI, R_PPC_ADDR16_HA and R_PPC_REL24 are
the types generated by the kpatch-build userspace tool or klp-convert
kernel tree observed applying a relocation to a post-init module.

Use patch_instruction() to patch those relocations.

Commit 8734b41b3e ("powerpc/module_64: Fix livepatching for
RO modules") did similar change in module_64.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/d5697157cb7dba3927e19aa17c915a83bc550bb2.1640017960.git.christophe.leroy@csgroup.eu
This commit is contained in:
Christophe Leroy 2021-12-20 16:38:09 +00:00 committed by Michael Ellerman
parent 2f293651ec
commit 0c850965d6
1 changed files with 30 additions and 14 deletions
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44
arch/powerpc/kernel/module_32.c
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@ -18,6 +18,7 @@
#include <linux/bug.h>
#include <linux/sort.h>
#include <asm/setup.h>
#include <asm/code-patching.h>
/* Count how many different relocations (different symbol, different
addend) */
@ -174,15 +175,25 @@ static uint32_t do_plt_call(void *location,
entry++;
}
entry->jump[0] = PPC_RAW_LIS(_R12, PPC_HA(val));
entry->jump[1] = PPC_RAW_ADDI(_R12, _R12, PPC_LO(val));
entry->jump[2] = PPC_RAW_MTCTR(_R12);
entry->jump[3] = PPC_RAW_BCTR();
if (patch_instruction(&entry->jump[0], ppc_inst(PPC_RAW_LIS(_R12, PPC_HA(val)))))
return 0;
if (patch_instruction(&entry->jump[1], ppc_inst(PPC_RAW_ADDI(_R12, _R12, PPC_LO(val)))))
return 0;
if (patch_instruction(&entry->jump[2], ppc_inst(PPC_RAW_MTCTR(_R12))))
return 0;
if (patch_instruction(&entry->jump[3], ppc_inst(PPC_RAW_BCTR())))
return 0;
pr_debug("Initialized plt for 0x%x at %p\n", val, entry);
return (uint32_t)entry;
}
static int patch_location_16(uint32_t *loc, u16 value)
{
loc = PTR_ALIGN_DOWN(loc, sizeof(u32));
return patch_instruction(loc, ppc_inst((*loc & 0xffff0000) | value));
}
int apply_relocate_add(Elf32_Shdr *sechdrs,
const char *strtab,
unsigned int symindex,
@ -216,37 +227,42 @@ int apply_relocate_add(Elf32_Shdr *sechdrs,
case R_PPC_ADDR16_LO:
/* Low half of the symbol */
*(uint16_t *)location = value;
if (patch_location_16(location, PPC_LO(value)))
return -EFAULT;
break;
case R_PPC_ADDR16_HI:
/* Higher half of the symbol */
*(uint16_t *)location = (value >> 16);
if (patch_location_16(location, PPC_HI(value)))
return -EFAULT;
break;
case R_PPC_ADDR16_HA:
/* Sign-adjusted lower 16 bits: PPC ELF ABI says:
(((x >> 16) + ((x & 0x8000) ? 1 : 0))) & 0xFFFF.
This is the same, only sane.
*/
*(uint16_t *)location = (value + 0x8000) >> 16;
if (patch_location_16(location, PPC_HA(value)))
return -EFAULT;
break;
case R_PPC_REL24:
if ((int)(value - (uint32_t)location) < -0x02000000
|| (int)(value - (uint32_t)location) >= 0x02000000)
|| (int)(value - (uint32_t)location) >= 0x02000000) {
value = do_plt_call(location, value,
sechdrs, module);
if (!value)
return -EFAULT;
}
/* Only replace bits 2 through 26 */
pr_debug("REL24 value = %08X. location = %08X\n",
value, (uint32_t)location);
pr_debug("Location before: %08X.\n",
*(uint32_t *)location);
*(uint32_t *)location
= (*(uint32_t *)location & ~0x03fffffc)
value = (*(uint32_t *)location & ~0x03fffffc)
| ((value - (uint32_t)location)
& 0x03fffffc);
if (patch_instruction(location, ppc_inst(value)))
return -EFAULT;
pr_debug("Location after: %08X.\n",
*(uint32_t *)location);
pr_debug("ie. jump to %08X+%08X = %08X\n",