[RESEND PATCH] powerpc/modules: Introduce new stub code for SHN_LIVEPATCH symbols
Kamalesh Babulal
kamalesh at linux.vnet.ibm.com
Tue Jun 27 14:30:18 AEST 2017
R_PPC64_REL24 relocation type is used for a function call, where the
function symbol address is resolved and stub code (a.k.a trampoline)
is constructed to jump into the global entry of the function. The
caller is responsible for setting up the TOC of the called function
before branching and NOP is expected after every branch, which gets
replaced with an instruction to restore the callers TOC from the
stack on return.
SHN_LIVEPATCH symbols with R_PPC64_REL24 relocation type might not
adhere to nop instruction after a branch. The reason being called
function was local to the callee and the instruction sequence
generated does not stores and restores the TOC value onto the stack
of the calling function, which is right. The calling function instead
uses the localentry (function entry + 0x8) to jump into the function
and returns without the need for store/restoring the TOC, as both of
the functions were in the same compilation unit.
When such functions become global because they are livepatched and
every call to the function, re-directs the callee to the patched
version in the module. Every branch from the livepatch module, to
previously local function turns out to be a jump into the kernel
code but with the code sequence remains that of the localentry. This
leads to error while trying to access the function with an assumption,
of being local to the calling function:
insmod: ERROR: could not insert module ./kpatch-meminfo-string.ko: Invalid module format
Jun 13 02:10:47 ubuntu kernel: [ 37.774292] module_64: kpatch_meminfo_string: REL24 -1152921504749690968 out of range!
SHN_LIVEPATCH symbols + R_PPC64_REL24 type relocations can be handled
by introducing a new stub code sequence, instead of regular module stub
code. Where stub takes care of storing and restoring the Link Register/TOC
onto the stack of the livepatched function and restores them upon
return from the called function.
Signed-off-by: Kamalesh Babulal <kamalesh at linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Balbir Singh <bsingharora at gmail.com>
Cc: Josh Poimboeuf <jpoimboe at redhat.com>
Cc: Jessica Yu <jeyu at kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth at linux.vnet.ibm.com>
Cc: Aravinda Prasad <aravinda at linux.vnet.ibm.com>
Cc: live-patching at vger.kernel.org
---
Resending the patch with minor editing of commit message and have added
more developers to cc list.
arch/powerpc/kernel/module_64.c | 55 ++++++++++++++++++++++++++++++++---------
1 file changed, 44 insertions(+), 11 deletions(-)
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 0b0f896..52ded0f 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -102,10 +102,16 @@ static unsigned int local_entry_offset(const Elf64_Sym *sym)
jump, actually, to reset r2 (TOC+0x8000). */
struct ppc64_stub_entry
{
- /* 28 byte jump instruction sequence (7 instructions). We only
- * need 6 instructions on ABIv2 but we always allocate 7 so
- * so we don't have to modify the trampoline load instruction. */
- u32 jump[7];
+ /* 28 byte jump instruction sequence (7 instructions) and only
+ * 6 instructions are needed on ABIv2 to create trampoline.
+ * Trampoline for livepatch symbol needs extra 7 instructions
+ * to save and restore LR, TOC values.
+ *
+ * To accommodate extra instructions required for livepatch
+ * entry, we allocate 15 instructions so we don't have to
+ * modify the trampoline load instruction.
+ */
+ u32 jump[15];
/* Used by ftrace to identify stubs */
u32 magic;
/* Data for the above code */
@@ -131,7 +137,7 @@ static u32 ppc64_stub_insns[] = {
0x396b0000, /* addi r11,r11, <low> */
/* Save current r2 value in magic place on the stack. */
0xf8410000|R2_STACK_OFFSET, /* std r2,R2_STACK_OFFSET(r1) */
- 0xe98b0020, /* ld r12,32(r11) */
+ 0xe98b0040, /* ld r12,64(r11) */
#ifdef PPC64_ELF_ABI_v1
/* Set up new r2 from function descriptor */
0xe84b0028, /* ld r2,40(r11) */
@@ -140,6 +146,24 @@ static u32 ppc64_stub_insns[] = {
0x4e800420 /* bctr */
};
+static u32 ppc64_klp_stub_insns[] = {
+ 0x3d620000, /* addis r11,r2, <high> */
+ 0x396b0000, /* addi r11,r11, <low> */
+ 0x7c0802a6, /* mflr r0 */
+ 0xf8010010, /* std r0,16(r1) */
+ /* Save current r2 value in magic place on the stack. */
+ 0xf8410000|R2_STACK_OFFSET, /* std r2,R2_STACK_OFFSET(r1) */
+ 0xe98b0040, /* ld r12,64(r11) */
+ 0xf821ffe1, /* stdu r1,-32(r1) */
+ 0x7d8903a6, /* mtctr r12 */
+ 0x4e800421, /* bctrl */
+ 0x38210020, /* addi r1,r1,32 */
+ 0xe8010010, /* ld r0,16(r1) */
+ 0xe8410000|R2_STACK_OFFSET, /* ld r2,R2_STACK_OFFSET(r1) */
+ 0x7c0803a6, /* mtlr r0 */
+ 0x4e800020 /* blr */
+};
+
#ifdef CONFIG_DYNAMIC_FTRACE
int module_trampoline_target(struct module *mod, unsigned long addr,
unsigned long *target)
@@ -392,11 +416,16 @@ static inline unsigned long my_r2(const Elf64_Shdr *sechdrs, struct module *me)
static inline int create_stub(const Elf64_Shdr *sechdrs,
struct ppc64_stub_entry *entry,
unsigned long addr,
- struct module *me)
+ struct module *me, int klp_symbol)
{
long reladdr;
- memcpy(entry->jump, ppc64_stub_insns, sizeof(ppc64_stub_insns));
+ memset(entry, 0, sizeof(*entry));
+ if (klp_symbol)
+ memcpy(entry->jump, ppc64_klp_stub_insns,
+ sizeof(ppc64_klp_stub_insns));
+ else
+ memcpy(entry->jump, ppc64_stub_insns, sizeof(ppc64_stub_insns));
/* Stub uses address relative to r2. */
reladdr = (unsigned long)entry - my_r2(sechdrs, me);
@@ -419,7 +448,7 @@ static inline int create_stub(const Elf64_Shdr *sechdrs,
stub to set up the TOC ptr (r2) for the function. */
static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
unsigned long addr,
- struct module *me)
+ struct module *me, int klp_symbol)
{
struct ppc64_stub_entry *stubs;
unsigned int i, num_stubs;
@@ -435,7 +464,7 @@ static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
return (unsigned long)&stubs[i];
}
- if (!create_stub(sechdrs, &stubs[i], addr, me))
+ if (!create_stub(sechdrs, &stubs[i], addr, me, klp_symbol))
return 0;
return (unsigned long)&stubs[i];
@@ -615,13 +644,17 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
/* FIXME: Handle weak symbols here --RR */
if (sym->st_shndx == SHN_UNDEF) {
/* External: go via stub */
- value = stub_for_addr(sechdrs, value, me);
+ value = stub_for_addr(sechdrs, value, me, 0);
if (!value)
return -ENOENT;
if (!restore_r2((u32 *)location + 1, me))
return -ENOEXEC;
squash_toc_save_inst(strtab + sym->st_name, value);
+ } else if (sym->st_shndx == SHN_LIVEPATCH) {
+ value = stub_for_addr(sechdrs, value, me, 1);
+ if (!value)
+ return -ENOENT;
} else
value += local_entry_offset(sym);
@@ -775,7 +808,7 @@ static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module
#else
static unsigned long create_ftrace_stub(const Elf64_Shdr *sechdrs, struct module *me)
{
- return stub_for_addr(sechdrs, (unsigned long)ftrace_caller, me);
+ return stub_for_addr(sechdrs, (unsigned long)ftrace_caller, me, 0);
}
#endif
--
2.7.4
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