From d30a0c8bf99f0e6a7d8c57bd4524039585ffbced Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Fri, 14 Dec 2007 15:56:01 -0500 Subject: ARM kprobes: don't let a single-stepped stmdb corrupt the exception stack If kprobes installs a breakpoint on a "stmdb sp!, {...}" instruction, and then single-step it by simulation from the exception context, it will corrupt the saved regs on the stack from the previous context. To avoid this, let's add an optional parameter to the svc_entry macro allowing for a hole to be created on the stack before saving the interrupted context, and use it in the undef_svc handler when kprobes is enabled. Signed-off-by: Nicolas Pitre --- arch/arm/kernel/entry-armv.S | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index 29dec080a60..12ecc817be3 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -112,8 +112,8 @@ common_invalid: #define SPFIX(code...) #endif - .macro svc_entry - sub sp, sp, #S_FRAME_SIZE + .macro svc_entry, stack_hole=0 + sub sp, sp, #(S_FRAME_SIZE + \stack_hole) SPFIX( tst sp, #4 ) SPFIX( bicne sp, sp, #4 ) stmib sp, {r1 - r12} @@ -121,7 +121,7 @@ common_invalid: ldmia r0, {r1 - r3} add r5, sp, #S_SP @ here for interlock avoidance mov r4, #-1 @ "" "" "" "" - add r0, sp, #S_FRAME_SIZE @ "" "" "" "" + add r0, sp, #(S_FRAME_SIZE + \stack_hole) SPFIX( addne r0, r0, #4 ) str r1, [sp] @ save the "real" r0 copied @ from the exception stack @@ -242,7 +242,14 @@ svc_preempt: .align 5 __und_svc: +#ifdef CONFIG_KPROBES + @ If a kprobe is about to simulate a "stmdb sp..." instruction, + @ it obviously needs free stack space which then will belong to + @ the saved context. + svc_entry 64 +#else svc_entry +#endif @ @ call emulation code, which returns using r9 if it has emulated -- cgit v1.2.3