[PATCH 5.15 147/177] powerpc/module_64: Fix livepatching for RO modules

Greg Kroah-Hartman
2021-12-20T15:01:03Z

From: Russell Currey <ruscur@russell.cc>

commit 8734b41b3efe0fc6082c1937b0e88556c396dc96 upstream.

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. Work around this by performing these
writes through the text poke area by using patch_instruction().

R_PPC_REL24 is the only relocation type generated by the kpatch-build
userspace tool or klp-convert kernel tree that I observed applying a
relocation to a post-init module.

A more comprehensive solution is planned, but using patch_instruction()
for R_PPC_REL24 on should serve as a sufficient fix.

This does have a performance impact, I observed ~15% overhead in
module_load() on POWER8 bare metal with checksum verification off.

Fixes: c35717c71e98 ("powerpc: Set ARCH_HAS_STRICT_MODULE_RWX")
Cc: stable@vger.kernel.org # v5.14+
Reported-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
[mpe: Check return codes from patch_instruction()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211214121248.777249-1-mpe@ellerman.id.au
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/kernel/module_64.c | 42 ++++++++++++++++++++++++++++++++--------
1 file changed, 34 insertions(+), 8 deletions(-)

--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -422,11 +422,17 @@ static inline int create_stub(const Elf6
const char *name)
{
long reladdr;
+ func_desc_t desc;
+ int i;

if (is_mprofile_ftrace_call(name))
return create_ftrace_stub(entry, addr, me);

- memcpy(entry->jump, ppc64_stub_insns, sizeof(ppc64_stub_insns));
+ for (i = 0; i < sizeof(ppc64_stub_insns) / sizeof(u32); i++) {
+ if (patch_instruction(&entry->jump[i],
+ ppc_inst(ppc64_stub_insns[i])))
+ return 0;
+ }

/* Stub uses address relative to r2. */
reladdr = (unsigned long)entry - my_r2(sechdrs, me);
@@ -437,10 +443,24 @@ static inline int create_stub(const Elf6
}
pr_debug("Stub %p get data from reladdr %li\n", entry, reladdr);

- entry->jump[0] |= PPC_HA(reladdr);
- entry->jump[1] |= PPC_LO(reladdr);
- entry->funcdata = func_desc(addr);
- entry->magic = STUB_MAGIC;
+ if (patch_instruction(&entry->jump[0],
+ ppc_inst(entry->jump[0] | PPC_HA(reladdr))))
+ return 0;
+
+ if (patch_instruction(&entry->jump[1],
+ ppc_inst(entry->jump[1] | PPC_LO(reladdr))))
+ return 0;
+
+ // func_desc_t is 8 bytes if ABIv2, else 16 bytes
+ desc = func_desc(addr);
+ for (i = 0; i < sizeof(func_desc_t) / sizeof(u32); i++) {
+ if (patch_instruction(((u32 *)&entry->funcdata) + i,
+ ppc_inst(((u32 *)(&desc))[i])))
+ return 0;
+ }
+
+ if (patch_instruction(&entry->magic, ppc_inst(STUB_MAGIC)))
+ return 0;

return 1;
}
@@ -495,8 +515,11 @@ static int restore_r2(const char *name,
me->name, *instruction, instruction);
return 0;
}
+
/* ld r2,R2_STACK_OFFSET(r1) */
- *instruction = PPC_INST_LD_TOC;
+ if (patch_instruction(instruction, ppc_inst(PPC_INST_LD_TOC)))
+ return 0;
+
return 1;
}

@@ -636,9 +659,12 @@ int apply_relocate_add(Elf64_Shdr *sechd
}

/* Only replace bits 2 through 26 */
- *(uint32_t *)location
- = (*(uint32_t *)location & ~0x03fffffc)
+ value = (*(uint32_t *)location & ~0x03fffffc)
| (value & 0x03fffffc);
+
+ if (patch_instruction((u32 *)location, ppc_inst(value)))
+ return -EFAULT;
+
break;

case R_PPC64_REL64: