renegade-project/linux-next
2
0
Fork 0
mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-30 08:04:13 +08:00
Code

powerpc/livepatch: Add live patching support on ppc64le

Browse Source 
Add the kconfig logic & assembly support for handling live patched
functions. This depends on DYNAMIC_FTRACE_WITH_REGS, which in turn
depends on the new -mprofile-kernel ftrace ABI, which is only supported
currently on ppc64le.

Live patching is handled by a special ftrace handler. This means it runs
from ftrace_caller(). The live patch handler modifies the NIP so as to
redirect the return from ftrace_caller() to the new patched function.

However there is one particularly tricky case we need to handle.

If a function A calls another function B, and it is known at link time
that they share the same TOC, then A will not save or restore its TOC,
and will call the local entry point of B.

When we live patch B, we replace it with a new function C, which may
not have the same TOC as A. At live patch time it's too late to modify A
to do the TOC save/restore, so the live patching code must interpose
itself between A and C, and do the TOC save/restore that A omitted.

An additionaly complication is that the livepatch code can not create a
stack frame in order to save the TOC. That is because if C takes > 8
arguments, or is varargs, A will have written the arguments for C in
A's stack frame.

To solve this, we introduce a "livepatch stack" which grows upward from
the base of the regular stack, and is used to store the TOC & LR when
calling a live patched function.

When the patched function returns, we retrieve the real LR & TOC from
the livepatch stack, restore them, and pop the livepatch "stack frame".

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Reviewed-by: Balbir Singh <bsingharora@gmail.com>
This commit is contained in:
Michael Ellerman 2016-03-24 22:04:05 +11:00
parent 5d31a96e6c
commit 85baa09549
3 changed files with 104 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/powerpc/Kconfig
View File

@ -159,6 +159,7 @@ config PPC
select ARCH_HAS_DEVMEM_IS_ALLOWED
select HAVE_ARCH_SECCOMP_FILTER
select ARCH_HAS_UBSAN_SANITIZE_ALL
select HAVE_LIVEPATCH if HAVE_DYNAMIC_FTRACE_WITH_REGS
config GENERIC_CSUM
def_bool CPU_LITTLE_ENDIAN
@ -1110,3 +1111,5 @@ config PPC_LIB_RHEAP
bool
source "arch/powerpc/kvm/Kconfig"
source "kernel/livepatch/Kconfig"

4
arch/powerpc/kernel/asm-offsets.c
View File

@ -86,6 +86,10 @@ int main(void)
DEFINE(KSP_LIMIT, offsetof(struct thread_struct, ksp_limit));
#endif /* CONFIG_PPC64 */
#ifdef CONFIG_LIVEPATCH
DEFINE(TI_livepatch_sp, offsetof(struct thread_info, livepatch_sp));
#endif
DEFINE(KSP, offsetof(struct thread_struct, ksp));
DEFINE(PT_REGS, offsetof(struct thread_struct, regs));
#ifdef CONFIG_BOOKE

97
arch/powerpc/kernel/entry_64.S
View File

@ -20,6 +20,7 @@
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/magic.h>
#include <asm/unistd.h>
#include <asm/processor.h>
#include <asm/page.h>
@ -1224,6 +1225,9 @@ _GLOBAL(ftrace_caller)
addi r3,r3,function_trace_op@toc@l
ld r5,0(r3)
#ifdef CONFIG_LIVEPATCH
mr r14,r7 /* remember old NIP */
#endif
/* Calculate ip from nip-4 into r3 for call below */
subi r3, r7, MCOUNT_INSN_SIZE
@ -1248,6 +1252,9 @@ ftrace_call:
/* Load ctr with the possibly modified NIP */
ld r3, _NIP(r1)
mtctr r3
#ifdef CONFIG_LIVEPATCH
cmpd r14,r3 /* has NIP been altered? */
#endif
/* Restore gprs */
REST_8GPRS(0,r1)
@ -1265,6 +1272,11 @@ ftrace_call:
ld r0, LRSAVE(r1)
mtlr r0
#ifdef CONFIG_LIVEPATCH
/* Based on the cmpd above, if the NIP was altered handle livepatch */
bne- livepatch_handler
#endif
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
stdu r1, -112(r1)
.globl ftrace_graph_call
@ -1281,6 +1293,91 @@ _GLOBAL(ftrace_graph_stub)
_GLOBAL(ftrace_stub)
blr
#ifdef CONFIG_LIVEPATCH
/*
* This function runs in the mcount context, between two functions. As
* such it can only clobber registers which are volatile and used in
* function linkage.
*
* We get here when a function A, calls another function B, but B has
* been live patched with a new function C.
*
* On entry:
* - we have no stack frame and can not allocate one
* - LR points back to the original caller (in A)
* - CTR holds the new NIP in C
* - r0 & r12 are free
*
* r0 can't be used as the base register for a DS-form load or store, so
* we temporarily shuffle r1 (stack pointer) into r0 and then put it back.
*/
livepatch_handler:
CURRENT_THREAD_INFO(r12, r1)
/* Save stack pointer into r0 */
mr r0, r1
/* Allocate 3 x 8 bytes */
ld r1, TI_livepatch_sp(r12)
addi r1, r1, 24
std r1, TI_livepatch_sp(r12)
/* Save toc & real LR on livepatch stack */
std r2, -24(r1)
mflr r12
std r12, -16(r1)
/* Store stack end marker */
lis r12, STACK_END_MAGIC@h
ori r12, r12, STACK_END_MAGIC@l
std r12, -8(r1)
/* Restore real stack pointer */
mr r1, r0
/* Put ctr in r12 for global entry and branch there */
mfctr r12
bctrl
/*
* Now we are returning from the patched function to the original
* caller A. We are free to use r0 and r12, and we can use r2 until we
* restore it.
*/
CURRENT_THREAD_INFO(r12, r1)
/* Save stack pointer into r0 */
mr r0, r1
ld r1, TI_livepatch_sp(r12)
/* Check stack marker hasn't been trashed */
lis r2, STACK_END_MAGIC@h
ori r2, r2, STACK_END_MAGIC@l
ld r12, -8(r1)
1: tdne r12, r2
EMIT_BUG_ENTRY 1b, __FILE__, __LINE__ - 1, 0
/* Restore LR & toc from livepatch stack */
ld r12, -16(r1)
mtlr r12
ld r2, -24(r1)
/* Pop livepatch stack frame */
CURRENT_THREAD_INFO(r12, r0)
subi r1, r1, 24
std r1, TI_livepatch_sp(r12)
/* Restore real stack pointer */
mr r1, r0
/* Return to original caller of live patched function */
blr
#endif
#else
_GLOBAL_TOC(_mcount)
/* Taken from output of objdump from lib64/glibc */