From 1a2f728b034a7fa20099532ee5a5509b80ac08a5 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Mon, 30 Aug 2021 05:42:27 -0400 Subject: [PATCH] parisc: fix crash with signals and alloca commit 030f653078316a9cc9ca6bd1b0234dcf858be35d upstream. I was debugging some crashes on parisc and I found out that there is a crash possibility if a function using alloca is interrupted by a signal. The reason for the crash is that the gcc alloca implementation leaves garbage in the upper 32 bits of the sp register. This normally doesn't matter (the upper bits are ignored because the PSW W-bit is clear), however the signal delivery routine in the kernel uses full 64 bits of sp and it fails with -EFAULT if the upper 32 bits are not zero. I created this program that demonstrates the problem: #include #include #include #include static __attribute__((noinline,noclone)) void aa(int *size) { void * volatile p = alloca(-*size); while (1) ; } static void handler(int sig) { write(1, "signal delivered\n", 17); _exit(0); } int main(void) { int size = -0x100; signal(SIGALRM, handler); alarm(1); aa(&size); } If you compile it with optimizations, it will crash. The "aa" function has this disassembly: 000106a0 : 106a0: 08 03 02 41 copy r3,r1 106a4: 08 1e 02 43 copy sp,r3 106a8: 6f c1 00 80 stw,ma r1,40(sp) 106ac: 37 dc 3f c1 ldo -20(sp),ret0 106b0: 0c 7c 12 90 stw ret0,8(r3) 106b4: 0f 40 10 9c ldw 0(r26),ret0 ; ret0 = 0x00000000FFFFFF00 106b8: 97 9c 00 7e subi 3f,ret0,ret0 ; ret0 = 0xFFFFFFFF0000013F 106bc: d7 80 1c 1a depwi 0,31,6,ret0 ; ret0 = 0xFFFFFFFF00000100 106c0: 0b 9e 0a 1e add,l sp,ret0,sp ; sp = 0xFFFFFFFFxxxxxxxx 106c4: e8 1f 1f f7 b,l,n 106c4 ,r0 This patch fixes the bug by truncating the "usp" variable to 32 bits. Signed-off-by: Mikulas Patocka Cc: stable@vger.kernel.org Signed-off-by: Helge Deller Signed-off-by: Greg Kroah-Hartman --- arch/parisc/kernel/signal.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/parisc/kernel/signal.c b/arch/parisc/kernel/signal.c index 02895a8f2c55..92223f9ff05c 100644 --- a/arch/parisc/kernel/signal.c +++ b/arch/parisc/kernel/signal.c @@ -238,6 +238,12 @@ setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs, #endif usp = (regs->gr[30] & ~(0x01UL)); +#ifdef CONFIG_64BIT + if (is_compat_task()) { + /* The gcc alloca implementation leaves garbage in the upper 32 bits of sp */ + usp = (compat_uint_t)usp; + } +#endif /*FIXME: frame_size parameter is unused, remove it. */ frame = get_sigframe(&ksig->ka, usp, sizeof(*frame));