From 5c45b5280196a92c4437f5648209c5bd3f08e882 Mon Sep 17 00:00:00 2001 From: Alan Modra Date: Wed, 6 Dec 2017 17:12:28 -0200 Subject: [PATCH] powerpc/modules: Fix alignment of .toc section in kernel modules powerpc64 gcc can generate code that offsets an address, to access part of an object in memory. If the address is a -mcmodel=medium toc pointer relative address then code like the following is possible. addis r9,r2,var@toc@ha ld r3,var@toc@l(r9) ld r4,(var+8)@toc@l(r9) This works fine so long as var is naturally aligned, *and* r2 is sufficiently aligned. If not, there is a possibility that the offset added to access var+8 wraps over a n*64k+32k boundary. Modules don't have any guarantee that r2 is sufficiently aligned. Moreover, code generated by older compilers generates a .toc section with 2**0 alignment, which can result in relocation failures at module load time even without the wrap problem. Thus, this patch links modules with an aligned .toc section (Makefile and module.lds changes), and forces alignment for out of tree modules or those without a .toc section (module_64.c changes). Signed-off-by: Alan Modra [desnesn: updated patch to apply to powerpc-next kernel v4.15 ] Signed-off-by: Desnes A. Nunes do Rosario [mpe: Fix out-of-tree build, swap -256 for ~0xff, reflow comment] Signed-off-by: Michael Ellerman --- arch/powerpc/Makefile | 1 + arch/powerpc/kernel/module.lds | 8 ++++++++ arch/powerpc/kernel/module_64.c | 16 +++++++++++----- 3 files changed, 20 insertions(+), 5 deletions(-) create mode 100644 arch/powerpc/kernel/module.lds diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile index 1381693a4a51..ccd2556bdb53 100644 --- a/arch/powerpc/Makefile +++ b/arch/powerpc/Makefile @@ -63,6 +63,7 @@ UTS_MACHINE := $(subst $(space),,$(machine-y)) ifdef CONFIG_PPC32 KBUILD_LDFLAGS_MODULE += arch/powerpc/lib/crtsavres.o else +KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/powerpc/kernel/module.lds ifeq ($(call ld-ifversion, -ge, 225000000, y),y) # Have the linker provide sfpr if possible. # There is a corresponding test in arch/powerpc/lib/Makefile diff --git a/arch/powerpc/kernel/module.lds b/arch/powerpc/kernel/module.lds new file mode 100644 index 000000000000..cea5dc124be4 --- /dev/null +++ b/arch/powerpc/kernel/module.lds @@ -0,0 +1,8 @@ +/* Force alignment of .toc section. */ +SECTIONS +{ + .toc 0 : ALIGN(256) + { + *(.got .toc) + } +} diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c index e6c011d56629..d056b745743d 100644 --- a/arch/powerpc/kernel/module_64.c +++ b/arch/powerpc/kernel/module_64.c @@ -339,8 +339,11 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr, char *p; if (strcmp(secstrings + sechdrs[i].sh_name, ".stubs") == 0) me->arch.stubs_section = i; - else if (strcmp(secstrings + sechdrs[i].sh_name, ".toc") == 0) + else if (strcmp(secstrings + sechdrs[i].sh_name, ".toc") == 0) { me->arch.toc_section = i; + if (sechdrs[i].sh_addralign < 8) + sechdrs[i].sh_addralign = 8; + } else if (strcmp(secstrings+sechdrs[i].sh_name,"__versions")==0) dedotify_versions((void *)hdr + sechdrs[i].sh_offset, sechdrs[i].sh_size); @@ -373,12 +376,15 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr, return 0; } -/* r2 is the TOC pointer: it actually points 0x8000 into the TOC (this - gives the value maximum span in an instruction which uses a signed - offset) */ +/* + * r2 is the TOC pointer: it actually points 0x8000 into the TOC (this gives the + * value maximum span in an instruction which uses a signed offset). Round down + * to a 256 byte boundary for the odd case where we are setting up r2 without a + * .toc section. + */ static inline unsigned long my_r2(const Elf64_Shdr *sechdrs, struct module *me) { - return sechdrs[me->arch.toc_section].sh_addr + 0x8000; + return (sechdrs[me->arch.toc_section].sh_addr & ~0xfful) + 0x8000; } /* Both low and high 16 bits are added as SIGNED additions, so if low