From: Peter Zijlstra peterz@infradead.org
In order to allow breakpoints to emulate call functions, they need to push the return address onto the stack. But because the breakpoint exception frame is added to the stack when the breakpoint is hit, there's no room to add the address onto the stack and return to the address of the emulated called funtion.
To handle this, copy the exception frame on entry of the breakpoint handler and have leave a gap that can be used to add a return address to the stack frame and return from the breakpoint to the emulated called function, allowing for that called function to return back to the location after the breakpoint was placed.
The helper functions were also added:
int3_emulate_push(): to push the address onto the gap in the stack int3_emulate_jmp(): changes the location of the regs->ip to return there. int3_emulate_call(): push the return address and change regs->ip
Cc: Andy Lutomirski luto@kernel.org Cc: Nicolai Stange nstange@suse.de Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@redhat.com Cc: Borislav Petkov bp@alien8.de Cc: "H. Peter Anvin" hpa@zytor.com Cc: the arch/x86 maintainers x86@kernel.org Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Jiri Kosina jikos@kernel.org Cc: Miroslav Benes mbenes@suse.cz Cc: Petr Mladek pmladek@suse.com Cc: Joe Lawrence joe.lawrence@redhat.com Cc: Shuah Khan shuah@kernel.org Cc: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Cc: Tim Chen tim.c.chen@linux.intel.com Cc: Sebastian Andrzej Siewior bigeasy@linutronix.de Cc: Mimi Zohar zohar@linux.ibm.com Cc: Juergen Gross jgross@suse.com Cc: Nick Desaulniers ndesaulniers@google.com Cc: Nayna Jain nayna@linux.ibm.com Cc: Masahiro Yamada yamada.masahiro@socionext.com Cc: Joerg Roedel jroedel@suse.de Cc: "open list:KERNEL SELFTEST FRAMEWORK" linux-kselftest@vger.kernel.org Cc: stable@vger.kernel.org Fixes: b700e7f03df5 ("livepatch: kernel: add support for live patching") Signed-off-by: *** Need Peter Zijlstra's SoB here! *** Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org --- arch/x86/entry/entry_32.S | 11 +++++++++++ arch/x86/entry/entry_64.S | 14 ++++++++++++-- arch/x86/include/asm/text-patching.h | 20 ++++++++++++++++++++ 3 files changed, 43 insertions(+), 2 deletions(-)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index d309f30cf7af..50bbf4035baf 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -1478,6 +1478,17 @@ ENTRY(int3) ASM_CLAC pushl $-1 # mark this as an int
+#ifdef CONFIG_VM86 + testl $X86_EFLAGS_VM, PT_EFLAGS(%esp) + jnz .Lfrom_usermode_no_gap +#endif + testl $SEGMENT_RPL_MASK, PT_CS(%esp) + jnz .Lfrom_usermode_no_gap + .rept 6 + pushl 5*4(%esp) + .endr +.Lfrom_usermode_no_gap: + SAVE_ALL switch_stacks=1 ENCODE_FRAME_POINTER TRACE_IRQS_OFF diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 1f0efdb7b629..834ec1397dab 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -879,7 +879,7 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt * @paranoid == 2 is special: the stub will never switch stacks. This is for * #DF: if the thread stack is somehow unusable, we'll still get a useful OOPS. */ -.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 +.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 create_gap=0 ENTRY(\sym) UNWIND_HINT_IRET_REGS offset=\has_error_code*8
@@ -899,6 +899,16 @@ ENTRY(\sym) jnz .Lfrom_usermode_switch_stack_@ .endif
+ .if \create_gap == 1 + testb $3, CS-ORIG_RAX(%rsp) + jnz .Lfrom_usermode_no_gap_@ + .rept 6 + pushq 5*8(%rsp) + .endr + UNWIND_HINT_IRET_REGS offset=8 +.Lfrom_usermode_no_gap_@: + .endif + .if \paranoid call paranoid_entry .else @@ -1130,7 +1140,7 @@ apicinterrupt3 HYPERV_STIMER0_VECTOR \ #endif /* CONFIG_HYPERV */
idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK -idtentry int3 do_int3 has_error_code=0 +idtentry int3 do_int3 has_error_code=0 create_gap=1 idtentry stack_segment do_stack_segment has_error_code=1
#ifdef CONFIG_XEN_PV diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h index e85ff65c43c3..ba275b6292db 100644 --- a/arch/x86/include/asm/text-patching.h +++ b/arch/x86/include/asm/text-patching.h @@ -39,4 +39,24 @@ extern int poke_int3_handler(struct pt_regs *regs); extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler); extern int after_bootmem;
+static inline void int3_emulate_push(struct pt_regs *regs, unsigned long val) +{ + regs->sp -= sizeof(unsigned long); + *(unsigned long *)regs->sp = val; +} + +static inline void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip) +{ + regs->ip = ip; +} + +#define INT3_INSN_SIZE 1 +#define CALL_INSN_SIZE 5 + +static inline void int3_emulate_call(struct pt_regs *regs, unsigned long func) +{ + int3_emulate_push(regs, regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE); + int3_emulate_jmp(regs, func); +} + #endif /* _ASM_X86_TEXT_PATCHING_H */