Re: [PATCH v4 15/16] module: Move where we mark modules RO,X

From: Peter Zijlstra
Date: Mon Oct 21 2019 - 12:12:24 EST

On Mon, Oct 21, 2019 at 05:34:25PM +0200, Peter Zijlstra wrote:
> On Mon, Oct 21, 2019 at 04:14:02PM +0200, Peter Zijlstra wrote:

> So On IRC Josh suggested we use text_poke() for RELA. Since KLP is only
> available on Power and x86, and Power does not have STRICT_MODULE_RWX,
> the below should be sufficient.
>
> Completely untested...

And because s390 also has: HAVE_LIVEPATCH and STRICT_MODULE_RWX the even
less tested s390 bits included below.

Heiko, apologies if I completely wrecked it.

The purpose is to remove module_disable_ro()/module_enable_ro() from
livepatch/core.c such that:

- nothing relies on where in the module loading path module text goes RX.
- nothing ever has writable text

> ---
> arch/x86/kernel/module.c | 40 +++++++++++++++++++++++++++++++++-------
> include/linux/livepatch.h | 7 +++++++
> kernel/livepatch/core.c | 14 ++++++++++----
> 3 files changed, 50 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
> index d5c72cb877b3..76fa2c5f2d7b 100644
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -126,11 +126,12 @@ int apply_relocate(Elf32_Shdr *sechdrs,
> return 0;
> }
> #else /*X86_64*/
> -int apply_relocate_add(Elf64_Shdr *sechdrs,
> +int __apply_relocate_add(Elf64_Shdr *sechdrs,
> const char *strtab,
> unsigned int symindex,
> unsigned int relsec,
> - struct module *me)
> + struct module *me,
> + void *(*write)(void *addr, const void *val, size_t size))
> {
> unsigned int i;
> Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
> @@ -162,19 +163,19 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> case R_X86_64_64:
> if (*(u64 *)loc != 0)
> goto invalid_relocation;
> - *(u64 *)loc = val;
> + write(loc, &val, 8);
> break;
> case R_X86_64_32:
> if (*(u32 *)loc != 0)
> goto invalid_relocation;
> - *(u32 *)loc = val;
> + write(loc, &val, 4);
> if (val != *(u32 *)loc)
> goto overflow;
> break;
> case R_X86_64_32S:
> if (*(s32 *)loc != 0)
> goto invalid_relocation;
> - *(s32 *)loc = val;
> + write(loc, &val, 4);
> if ((s64)val != *(s32 *)loc)
> goto overflow;
> break;
> @@ -183,7 +184,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> if (*(u32 *)loc != 0)
> goto invalid_relocation;
> val -= (u64)loc;
> - *(u32 *)loc = val;
> + write(loc, &val, 4);
> #if 0
> if ((s64)val != *(s32 *)loc)
> goto overflow;
> @@ -193,7 +194,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> if (*(u64 *)loc != 0)
> goto invalid_relocation;
> val -= (u64)loc;
> - *(u64 *)loc = val;
> + write(loc, &val, 8);
> break;
> default:
> pr_err("%s: Unknown rela relocation: %llu\n",
> @@ -215,6 +216,31 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> me->name);
> return -ENOEXEC;
> }
> +
> +int apply_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> + return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, memcpy);
> +}
> +
> +int klp_apply_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> + int ret;
> +
> + ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, text_poke);
> + if (!ret)
> + text_poke_sync();
> +
> + return ret;
> +}
> +
> #endif
>
> int module_finalize(const Elf_Ehdr *hdr,
> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> index 273400814020..5b8c10871b70 100644
> --- a/include/linux/livepatch.h
> +++ b/include/linux/livepatch.h
> @@ -217,6 +217,13 @@ void *klp_shadow_get_or_alloc(void *obj, unsigned long id,
> void klp_shadow_free(void *obj, unsigned long id, klp_shadow_dtor_t dtor);
> void klp_shadow_free_all(unsigned long id, klp_shadow_dtor_t dtor);
>
> +
> +extern int klp_apply_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me);
> +
> #else /* !CONFIG_LIVEPATCH */
>
> static inline int klp_module_coming(struct module *mod) { return 0; }
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index ab4a4606d19b..e690519aba31 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -245,6 +245,15 @@ static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod)
> return 0;
> }
>
> +int __weak klp_apply_relocate_add(Elf64_Shdr *sechdrs,
> + const char *strtab,
> + unsigned int symindex,
> + unsigned int relsec,
> + struct module *me)
> +{
> + apply_relocate_add(sechdrs, strtab, symindex, relsec, me);
> +}
> +
> static int klp_write_object_relocations(struct module *pmod,
> struct klp_object *obj)
> {
> @@ -285,7 +294,7 @@ static int klp_write_object_relocations(struct module *pmod,
> if (ret)
> break;
>
> - ret = apply_relocate_add(pmod->klp_info->sechdrs,
> + ret = klp_apply_relocate_add(pmod->klp_info->sechdrs,
> pmod->core_kallsyms.strtab,
> pmod->klp_info->symndx, i, pmod);
> if (ret)
> @@ -721,16 +730,13 @@ static int klp_init_object_loaded(struct klp_patch *patch,
>
> mutex_lock(&text_mutex);
>
> - module_disable_ro(patch->mod);
> ret = klp_write_object_relocations(patch->mod, obj);
> if (ret) {
> - module_enable_ro(patch->mod, true);
> mutex_unlock(&text_mutex);
> return ret;
> }
>
> arch_klp_init_object_loaded(patch, obj);
> - module_enable_ro(patch->mod, true);
>
> mutex_unlock(&text_mutex);
>

diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c
index ba8f19bb438b..5f3443098172 100644
--- a/arch/s390/kernel/module.c
+++ b/arch/s390/kernel/module.c
@@ -174,7 +174,8 @@ 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 *addr, const char *data, size_t len))
{
unsigned long umax;
long min, max;
@@ -194,26 +195,29 @@ 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) {
+ write(loc, &val, 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(loc, &tmp, 2);
+ } else if (bits == 16) {
+ write(loc, &val, 2);
+ } else if (bits == 20) {
+ unsigned int tmp = (val & 0xfff) << 16 |
+ (val & 0xff000) >> 4 | (*(unsigned int *) loc & 0xf00000ff);
+ write(loc, &tmp, 4);
+ } else if (bits == 32) {
+ write(loc, &val, 4);
+ } else if (bits == 64) {
+ write(loc, &val, 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 *addr, const void *data, size_t len))
{
struct mod_arch_syminfo *info;
Elf_Addr loc, val;
@@ -241,17 +245,17 @@ 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 +264,15 @@ 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. */
@@ -293,23 +297,23 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
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. */
@@ -357,17 +361,17 @@ 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 +379,20 @@ 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 +416,10 @@ 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,
+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 *addr, const void *data, size_t len))
{
Elf_Addr base;
Elf_Sym *symtab;
@@ -437,6 +442,25 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
return 0;
}

+static void memwrite(void *addr, const void *data, size_t len)
+{
+ memcpy(addr, data, len);
+}
+
+int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
+ unsigned int symindex, unsigned int relsec,
+ struct module *me)
+{
+ return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, memwrite);
+}
+
+int klp_apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
+ unsigned int symindex, unsigned int relsec,
+ struct module *me)
+{
+ return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me, s390_kernel_write);
+}
+
int module_finalize(const Elf_Ehdr *hdr,
const Elf_Shdr *sechdrs,
struct module *me)