On Thu, 14 Apr 2022 at 15:23, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
From: Ard Biesheuvel ardb@kernel.org
[ Upstream commit d11967870815b5ab89843980e35aab616c97c463 ]
NAK. Please don't backport these patches to -stable, I thought I had been clear on this.
Tweak the ftrace return paths to avoid redundant loads of SP, as well as unnecessary clobbering of IP.
This also fixes the inconsistency of using MOV to perform a function return, which is sub-optimal on recent micro-architectures but more importantly, does not perform an interworking return, unlike compiler generated function returns in Thumb2 builds.
Let's fix this by popping PC from the stack like most ordinary code does.
Signed-off-by: Ard Biesheuvel ardb@kernel.org Reviewed-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Sasha Levin sashal@kernel.org
arch/arm/kernel/entry-ftrace.S | 51 +++++++++++++++------------------- 1 file changed, 22 insertions(+), 29 deletions(-)
diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S index 1acf4d05e94c..393c342ecd51 100644 --- a/arch/arm/kernel/entry-ftrace.S +++ b/arch/arm/kernel/entry-ftrace.S @@ -41,10 +41,7 @@
- mcount can be thought of as a function called in the middle of a subroutine
- call. As such, it needs to be transparent for both the caller and the
- callee: the original lr needs to be restored when leaving mcount, and no
- registers should be clobbered. (In the __gnu_mcount_nc implementation, we
- clobber the ip register. This is OK because the ARM calling convention
- allows it to be clobbered in subroutines and doesn't use it to hold
- parameters.)
- registers should be clobbered.
- When using dynamic ftrace, we patch out the mcount call by a "mov r0, r0"
- for the mcount case, and a "pop {lr}" for the __gnu_mcount_nc case (see
@@ -96,26 +93,25 @@
.macro __ftrace_regs_caller
sub sp, sp, #8 @ space for PC and CPSR OLD_R0,
str lr, [sp, #-8]! @ store LR as PC and make space for CPSR/OLD_R0, @ OLD_R0 will overwrite previous LR
add ip, sp, #12 @ move in IP the value of SP as it was@ before the push {lr} of the mcount mechanism
ldr lr, [sp, #8] @ get previous LR
str lr, [sp, #0] @ store LR instead of PC
str r0, [sp, #8] @ write r0 as OLD_R0 over previous LR
ldr lr, [sp, #8] @ get previous LR
str lr, [sp, #-4]! @ store previous LR as LR
str r0, [sp, #8] @ write r0 as OLD_R0 over previous LR
add lr, sp, #16 @ move in LR the value of SP as it was@ before the push {lr} of the mcount mechanism
stmdb sp!, {ip, lr}stmdb sp!, {r0-r11, lr}
push {r0-r11, ip, lr} @ stack content at this point: @ 0 4 48 52 56 60 64 68 72
@ R0 | R1 | ... | LR | SP + 4 | previous LR | LR | PSR | OLD_R0 |
@ R0 | R1 | ... | IP | SP + 4 | previous LR | LR | PSR | OLD_R0 |
mov r3, sp @ struct pt_regs*
mov r3, sp @ struct pt_regs* ldr r2, =function_trace_op ldr r2, [r2] @ pointer to the current@@ -138,11 +134,9 @@ ftrace_graph_regs_call: #endif
@ pop saved regs
ldmia sp!, {r0-r12} @ restore r0 through r12ldr ip, [sp, #8] @ restore PCldr lr, [sp, #4] @ restore LRldr sp, [sp, #0] @ restore SPmov pc, ip @ return
pop {r0-r11, ip, lr} @ restore r0 through r12ldr lr, [sp], #4 @ restore LRldr pc, [sp], #12.endm
#ifdef CONFIG_FUNCTION_GRAPH_TRACER @@ -158,11 +152,9 @@ ftrace_graph_regs_call: bl prepare_ftrace_return
@ pop registers saved in ftrace_regs_caller
ldmia sp!, {r0-r12} @ restore r0 through r12ldr ip, [sp, #8] @ restore PCldr lr, [sp, #4] @ restore LRldr sp, [sp, #0] @ restore SPmov pc, ip @ return
pop {r0-r11, ip, lr} @ restore r0 through r12ldr lr, [sp], #4 @ restore LRldr pc, [sp], #12.endm #endif @@ -273,16 +265,17 @@ ENDPROC(ftrace_graph_caller_old) .endm
.macro mcount_exit
ldmia sp!, {r0-r3, ip, lr}ret ip
ldmia sp!, {r0-r3}ldr lr, [sp, #4]ldr pc, [sp], #8.endm
ENTRY(__gnu_mcount_nc) UNWIND(.fnstart) #ifdef CONFIG_DYNAMIC_FTRACE
mov ip, lrldmia sp!, {lr}ret ip
push {lr}ldr lr, [sp, #4]ldr pc, [sp], #8#else __mcount
#endif
2.34.1