The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 67147e96a332b56c7206238162771d82467f86c0 Mon Sep 17 00:00:00 2001
From: Heiko Carstens hca@linux.ibm.com Date: Fri, 18 Jun 2021 16:58:47 +0200 Subject: [PATCH] s390/stack: fix possible register corruption with stack switch helper
The CALL_ON_STACK macro is used to call a C function from inline assembly, and therefore must consider the C ABI, which says that only registers 6-13, and 15 are non-volatile (restored by the called function).
The inline assembly incorrectly marks all registers used to pass parameters to the called function as read-only input operands, instead of operands that are read and written to. This might result in register corruption depending on usage, compiler, and compile options.
Fix this by marking all operands used to pass parameters as read/write operands. To keep the code simple even register 6, if used, is marked as read-write operand.
Fixes: ff340d2472ec ("s390: add stack switch helper") Cc: stable@kernel.org # 4.20 Reviewed-by: Vasily Gorbik gor@linux.ibm.com Signed-off-by: Heiko Carstens hca@linux.ibm.com Signed-off-by: Vasily Gorbik gor@linux.ibm.com
diff --git a/arch/s390/include/asm/stacktrace.h b/arch/s390/include/asm/stacktrace.h index 2b543163d90a..76c6034428be 100644 --- a/arch/s390/include/asm/stacktrace.h +++ b/arch/s390/include/asm/stacktrace.h @@ -91,12 +91,16 @@ struct stack_frame { CALL_ARGS_4(arg1, arg2, arg3, arg4); \ register unsigned long r4 asm("6") = (unsigned long)(arg5)
-#define CALL_FMT_0 "=&d" (r2) : -#define CALL_FMT_1 "+&d" (r2) : -#define CALL_FMT_2 CALL_FMT_1 "d" (r3), -#define CALL_FMT_3 CALL_FMT_2 "d" (r4), -#define CALL_FMT_4 CALL_FMT_3 "d" (r5), -#define CALL_FMT_5 CALL_FMT_4 "d" (r6), +/* + * To keep this simple mark register 2-6 as being changed (volatile) + * by the called function, even though register 6 is saved/nonvolatile. + */ +#define CALL_FMT_0 "=&d" (r2) +#define CALL_FMT_1 "+&d" (r2) +#define CALL_FMT_2 CALL_FMT_1, "+&d" (r3) +#define CALL_FMT_3 CALL_FMT_2, "+&d" (r4) +#define CALL_FMT_4 CALL_FMT_3, "+&d" (r5) +#define CALL_FMT_5 CALL_FMT_4, "+&d" (r6)
#define CALL_CLOBBER_5 "0", "1", "14", "cc", "memory" #define CALL_CLOBBER_4 CALL_CLOBBER_5 @@ -118,7 +122,7 @@ struct stack_frame { " brasl 14,%[_fn]\n" \ " la 15,0(%[_prev])\n" \ : [_prev] "=&a" (prev), CALL_FMT_##nr \ - [_stack] "R" (stack), \ + : [_stack] "R" (stack), \ [_bc] "i" (offsetof(struct stack_frame, back_chain)), \ [_frame] "d" (frame), \ [_fn] "X" (fn) : CALL_CLOBBER_##nr); \