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: