[PATCH v2 2/2] powerpc/module_64: Use patch_memory() to apply relocations to loaded modules
Christophe Leroy
christophe.leroy at csgroup.eu
Sun Dec 12 21:41:05 AEDT 2021
Le 12/12/2021 à 02:03, Russell Currey a écrit :
> 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_memory().
>
> Similar to x86 and s390 implementations, apply_relocate_add() now
> chooses to use patch_memory() or memcpy() depending on if the module
> is loaded or not. Without STRICT_KERNEL_RWX, patch_memory() is just
> memcpy(), so there should be no performance impact.
>
> While many relocation types may not be applied in a livepatch
> context, comprehensively handling them prevents any issues in future,
> with no performance penalty as the text poke area is only used when
> necessary.
>
> create_stub() and create_ftrace_stub() are modified to first write
> to the stack so that the ppc64_stub_entry struct only takes one
> write() to modify, saving several map/unmap/flush operations
> when use of patch_memory() is necessary.
>
> This patch also contains some trivial whitespace fixes.
>
> Fixes: c35717c71e98 ("powerpc: Set ARCH_HAS_STRICT_MODULE_RWX")
> Reported-by: Joe Lawrence <joe.lawrence at redhat.com>
> Signed-off-by: Russell Currey <ruscur at russell.cc>
> ---
> v2: No changes.
>
> Some discussion here:https://github.com/linuxppc/issues/issues/375
> for-stable version using patch_instruction():
> https://lore.kernel.org/linuxppc-dev/20211123081520.18843-1-ruscur@russell.cc/
>
> arch/powerpc/kernel/module_64.c | 157 +++++++++++++++++++++-----------
> 1 file changed, 104 insertions(+), 53 deletions(-)
>
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index 6baa676e7cb6..2a146750fa6f 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -350,11 +350,11 @@ static u32 stub_insns[] = {
> */
> static inline int create_ftrace_stub(struct ppc64_stub_entry *entry,
> unsigned long addr,
> - struct module *me)
> + struct module *me,
> + void *(*write)(void *, const void *, size_t))
I really dislike this write() parameter to the function.
I think it would be better to define a static sub-function that takes
write()'s parameters plus the 'struct module *me' and have it call
either patch_memory() or memcpy() based on me->state.
> {
> long reladdr;
> -
> - memcpy(entry->jump, stub_insns, sizeof(stub_insns));
> + struct ppc64_stub_entry tmp_entry;
>
> /* Stub uses address relative to kernel toc (from the paca) */
> reladdr = addr - kernel_toc_addr();
> @@ -364,12 +364,20 @@ static inline int create_ftrace_stub(struct ppc64_stub_entry *entry,
> return 0;
> }
>
> - entry->jump[1] |= PPC_HA(reladdr);
> - entry->jump[2] |= PPC_LO(reladdr);
> + /*
> + * In case @entry is write-protected, make our changes on the stack
> + * so we can update the whole struct in one write().
> + */
> + memcpy(&tmp_entry, entry, sizeof(struct ppc64_stub_entry));
That copy seems unnecessary, entry is a struct with three fields and you
are setting all three field below.
>
> + memcpy(&tmp_entry.jump, stub_insns, sizeof(stub_insns));
> + tmp_entry.jump[1] |= PPC_HA(reladdr);
> + tmp_entry.jump[2] |= PPC_LO(reladdr);
> /* Eventhough we don't use funcdata in the stub, it's needed elsewhere. */
> - entry->funcdata = func_desc(addr);
> - entry->magic = STUB_MAGIC;
> + tmp_entry.funcdata = func_desc(addr);
> + tmp_entry.magic = STUB_MAGIC;
> +
> + write(entry, &tmp_entry, sizeof(struct ppc64_stub_entry));
>
> return 1;
> }
> @@ -392,7 +400,8 @@ static bool is_mprofile_ftrace_call(const char *name)
> #else
> static inline int create_ftrace_stub(struct ppc64_stub_entry *entry,
> unsigned long addr,
> - struct module *me)
> + struct module *me,
> + void *(*write)(void *, const void *, size_t))
> {
> return 0;
> }
> @@ -419,14 +428,14 @@ static inline int create_stub(const Elf64_Shdr *sechdrs,
> struct ppc64_stub_entry *entry,
> unsigned long addr,
> struct module *me,
> - const char *name)
> + const char *name,
> + void *(*write)(void *, const void *, size_t))
> {
> long reladdr;
> + struct ppc64_stub_entry tmp_entry;
>
> if (is_mprofile_ftrace_call(name))
> - return create_ftrace_stub(entry, addr, me);
> -
> - memcpy(entry->jump, ppc64_stub_insns, sizeof(ppc64_stub_insns));
> + return create_ftrace_stub(entry, addr, me, write);
>
> /* Stub uses address relative to r2. */
> reladdr = (unsigned long)entry - my_r2(sechdrs, me);
> @@ -437,10 +446,19 @@ static inline int create_stub(const Elf64_Shdr *sechdrs,
> }
> 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;
> + /*
> + * In case @entry is write-protected, make our changes on the stack
> + * so we can update the whole struct in one write().
> + */
> + memcpy(&tmp_entry, entry, sizeof(struct ppc64_stub_entry));
> +
> + memcpy(&tmp_entry.jump, ppc64_stub_insns, sizeof(ppc64_stub_insns));
> + tmp_entry.jump[0] |= PPC_HA(reladdr);
> + tmp_entry.jump[1] |= PPC_LO(reladdr);
> + tmp_entry.funcdata = func_desc(addr);
> + tmp_entry.magic = STUB_MAGIC;
> +
> + write(entry, &tmp_entry, sizeof(struct ppc64_stub_entry));
>
> return 1;
> }
> @@ -450,7 +468,8 @@ static inline int create_stub(const Elf64_Shdr *sechdrs,
> static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
> unsigned long addr,
> struct module *me,
> - const char *name)
> + const char *name,
> + void *(*write)(void *, const void *, size_t))
> {
> struct ppc64_stub_entry *stubs;
> unsigned int i, num_stubs;
> @@ -467,7 +486,7 @@ static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
> return (unsigned long)&stubs[i];
> }
>
> - if (!create_stub(sechdrs, &stubs[i], addr, me, name))
> + if (!create_stub(sechdrs, &stubs[i], addr, me, name, write))
> return 0;
>
> return (unsigned long)&stubs[i];
> @@ -496,15 +515,20 @@ static int restore_r2(const char *name, u32 *instruction, struct module *me)
> return 0;
> }
> /* ld r2,R2_STACK_OFFSET(r1) */
> - *instruction = PPC_INST_LD_TOC;
> + if (me->state == MODULE_STATE_UNFORMED)
> + *instruction = PPC_INST_LD_TOC;
> + else
> + patch_instruction(instruction, ppc_inst(PPC_INST_LD_TOC));
> +
Would be better if that hunk was following the same approach as other
places.
> return 1;
> }
>
> -int apply_relocate_add(Elf64_Shdr *sechdrs,
> - const char *strtab,
> - unsigned int symindex,
> - unsigned int relsec,
> - struct module *me)
> +static int __apply_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me,
> + void *(*write)(void *dest, const void *src, size_t len))
> {
> unsigned int i;
> Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
> @@ -544,16 +568,17 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> switch (ELF64_R_TYPE(rela[i].r_info)) {
> case R_PPC64_ADDR32:
> /* Simply set it */
> - *(u32 *)location = value;
> + write(location, &value, 4);
> break;
>
> case R_PPC64_ADDR64:
> /* Simply set it */
> - *(unsigned long *)location = value;
> + write(location, &value, 8);
> break;
>
> case R_PPC64_TOC:
> - *(unsigned long *)location = my_r2(sechdrs, me);
> + value = my_r2(sechdrs, me);
> + write(location, &value, 8);
> break;
>
> case R_PPC64_TOC16:
> @@ -564,17 +589,17 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> me->name, value);
> return -ENOEXEC;
> }
> - *((uint16_t *) location)
> - = (*((uint16_t *) location) & ~0xffff)
> + value = (*((uint16_t *) location) & ~0xffff)
> | (value & 0xffff);
> + write(location, &value, 2);
> break;
>
> case R_PPC64_TOC16_LO:
> /* Subtract TOC pointer */
> value -= my_r2(sechdrs, me);
> - *((uint16_t *) location)
> - = (*((uint16_t *) location) & ~0xffff)
> + value = (*((uint16_t *) location) & ~0xffff)
> | (value & 0xffff);
> + write(location, &value, 2);
> break;
>
> case R_PPC64_TOC16_DS:
> @@ -585,9 +610,9 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> me->name, value);
> return -ENOEXEC;
> }
> - *((uint16_t *) location)
> - = (*((uint16_t *) location) & ~0xfffc)
> + value = (*((uint16_t *) location) & ~0xfffc)
> | (value & 0xfffc);
> + write(location, &value, 2);
> break;
>
> case R_PPC64_TOC16_LO_DS:
> @@ -598,18 +623,18 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> me->name, value);
> return -ENOEXEC;
> }
> - *((uint16_t *) location)
> - = (*((uint16_t *) location) & ~0xfffc)
> + value = (*((uint16_t *) location) & ~0xfffc)
> | (value & 0xfffc);
> + write(location, &value, 2);
> break;
>
> case R_PPC64_TOC16_HA:
> /* Subtract TOC pointer */
> value -= my_r2(sechdrs, me);
> value = ((value + 0x8000) >> 16);
> - *((uint16_t *) location)
> - = (*((uint16_t *) location) & ~0xffff)
> + value = (*((uint16_t *) location) & ~0xffff)
> | (value & 0xffff);
> + write(location, &value, 2);
> break;
>
> case R_PPC_REL24:
> @@ -618,14 +643,15 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> sym->st_shndx == SHN_LIVEPATCH) {
> /* External: go via stub */
> value = stub_for_addr(sechdrs, value, me,
> - strtab + sym->st_name);
> + strtab + sym->st_name, write);
> if (!value)
> return -ENOENT;
> if (!restore_r2(strtab + sym->st_name,
> (u32 *)location + 1, me))
> return -ENOEXEC;
> - } else
> + } else {
> value += local_entry_offset(sym);
> + }
>
> /* Convert value to relative */
> value -= (unsigned long)location;
> @@ -636,14 +662,15 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> }
>
> /* Only replace bits 2 through 26 */
> - *(uint32_t *)location
> - = (*(uint32_t *)location & ~0x03fffffc)
> + value = (*(uint32_t *)location & ~0x03fffffc)
> | (value & 0x03fffffc);
> + write(location, &value, 4);
> break;
>
> case R_PPC64_REL64:
> /* 64 bits relative (used by features fixups) */
> - *location = value - (unsigned long)location;
> + value -= (unsigned long)location;
> + write(location, &value, 8);
> break;
>
> case R_PPC64_REL32:
> @@ -655,7 +682,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> me->name, (long int)value);
> return -ENOEXEC;
> }
> - *(u32 *)location = value;
> + write(location, &value, 4);
> break;
>
> case R_PPC64_TOCSAVE:
> @@ -676,7 +703,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> break;
> /*
> * Check for the large code model prolog sequence:
> - * ld r2, ...(r12)
> + * ld r2, ...(r12)
> * add r2, r2, r12
> */
> if ((((uint32_t *)location)[0] & ~0xfffc) != PPC_RAW_LD(_R2, _R12, 0))
> @@ -688,25 +715,27 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> * addis r2, r12, (.TOC.-func)@ha
> * addi r2, r2, (.TOC.-func)@l
> */
> - ((uint32_t *)location)[0] = PPC_RAW_ADDIS(_R2, _R12, PPC_HA(value));
> - ((uint32_t *)location)[1] = PPC_RAW_ADDI(_R2, _R2, PPC_LO(value));
> + patch_instruction(&((uint32_t *)location)[0],
> + ppc_inst(PPC_RAW_ADDIS(_R2, _R12, PPC_HA(value))));
> + patch_instruction(&((uint32_t *)location)[1],
> + ppc_inst(PPC_RAW_ADDI(_R2, _R2, PPC_LO(value))));
Shouldn't you do like restore_r2() ?
> break;
>
> case R_PPC64_REL16_HA:
> /* Subtract location pointer */
> value -= (unsigned long)location;
> value = ((value + 0x8000) >> 16);
> - *((uint16_t *) location)
> - = (*((uint16_t *) location) & ~0xffff)
> + value = (*((uint16_t *) location) & ~0xffff)
> | (value & 0xffff);
> + write(location, &value, 2);
> break;
>
> case R_PPC64_REL16_LO:
> /* Subtract location pointer */
> value -= (unsigned long)location;
> - *((uint16_t *) location)
> - = (*((uint16_t *) location) & ~0xffff)
> + value = (*((uint16_t *) location) & ~0xffff)
> | (value & 0xffff);
> + write(location, &value, 2);
> break;
>
> default:
> @@ -720,6 +749,20 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> return 0;
> }
>
> +int apply_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> + void *(*write)(void *, const void *, size_t) = memcpy;
> + bool early = me->state == MODULE_STATE_UNFORMED;
> +
> + if (!early)
> + write = patch_memory;
> +
> + return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, write);
> +}
I really dislike this stuff with the write() function as a parameter. We
have 'me', it should be enough for the callee to know what to do, see my
first comment at the top of this email.
> #ifdef CONFIG_DYNAMIC_FTRACE
> int module_trampoline_target(struct module *mod, unsigned long addr,
> unsigned long *target)
> @@ -749,7 +792,7 @@ int module_trampoline_target(struct module *mod, unsigned long addr,
> if (copy_from_kernel_nofault(&funcdata, &stub->funcdata,
> sizeof(funcdata))) {
> pr_err("%s: fault reading funcdata for stub %lx for %s\n", __func__, addr, mod->name);
> - return -EFAULT;
> + return -EFAULT;
> }
>
> *target = stub_func_addr(funcdata);
> @@ -759,15 +802,23 @@ int module_trampoline_target(struct module *mod, unsigned long addr,
>
> int module_finalize_ftrace(struct module *mod, const Elf_Shdr *sechdrs)
> {
> + void *(*write)(void *, const void *, size_t) = memcpy;
> + bool early = mod->state == MODULE_STATE_UNFORMED;
> +
> + if (!early)
> + write = patch_memory;
> +
> mod->arch.tramp = stub_for_addr(sechdrs,
> (unsigned long)ftrace_caller,
> mod,
> - "ftrace_caller");
> + "ftrace_caller",
> + write);
> #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> mod->arch.tramp_regs = stub_for_addr(sechdrs,
> (unsigned long)ftrace_regs_caller,
> mod,
> - "ftrace_regs_caller");
> + "ftrace_regs_caller",
> + write);
> if (!mod->arch.tramp_regs)
> return -ENOENT;
> #endif
>
Christophe
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