| Message ID | alpine.LRH.2.02.2108291530440.5661@file01.intranet.prod.int.rdu2.redhat.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | parisc: fix crash with signals and alloca | expand |
On 8/29/21 9:50 PM, Mikulas Patocka wrote: > Hi > > 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 <stdlib.h> > #include <unistd.h> > #include <signal.h> > #include <alloca.h> > > 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 <aa>: > 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 <aa+0x24>,r0 > > This patch fixes the bug by truncating the "frame" variable to 32 bits. > > Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> > Cc: stable@vger.kernel.org > > --- > arch/parisc/kernel/signal.c | 5 +++++ > 1 file changed, 5 insertions(+) > > Index: linux-5.12/arch/parisc/kernel/signal.c > =================================================================== > --- linux-5.12.orig/arch/parisc/kernel/signal.c 2021-08-29 19:06:33.000000000 +0200 > +++ linux-5.12/arch/parisc/kernel/signal.c 2021-08-29 21:17:55.000000000 +0200 > @@ -246,6 +246,11 @@ setup_rt_frame(struct ksignal *ksig, sig > > #ifdef CONFIG_64BIT > > + if (is_compat_task()) { > + /* The gcc alloca implementation leaves garbage in the upper 32 bits of sp.*/ > + frame = (struct rt_sigframe __user *)(unsigned long)ptr_to_compat(frame); > + } > + Very good catch!!!! I'm just wondering if we miss to clip the sp somewhere earlier in the kernel call chain (e.g. in the irq/entry handlers), or if the clipping should be done somewhere else, e.g. some lines above here... Helge > compat_frame = (struct compat_rt_sigframe __user *)frame; > > if (is_compat_task()) { >
On 2021-08-29 4:46 p.m., Helge Deller wrote: > I'm just wondering if we miss to clip the sp somewhere earlier in the > kernel call chain (e.g. in the irq/entry handlers), or if the clipping > should be done somewhere else, e.g. some lines above here... Maybe sp should be clipped in get_stack_use_cr30? Dave
Index: linux-5.12/arch/parisc/kernel/signal.c =================================================================== --- linux-5.12.orig/arch/parisc/kernel/signal.c 2021-08-29 19:06:33.000000000 +0200 +++ linux-5.12/arch/parisc/kernel/signal.c 2021-08-29 21:17:55.000000000 +0200 @@ -246,6 +246,11 @@ setup_rt_frame(struct ksignal *ksig, sig #ifdef CONFIG_64BIT + if (is_compat_task()) { + /* The gcc alloca implementation leaves garbage in the upper 32 bits of sp.*/ + frame = (struct rt_sigframe __user *)(unsigned long)ptr_to_compat(frame); + } + compat_frame = (struct compat_rt_sigframe __user *)frame; if (is_compat_task()) {
Hi 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 <stdlib.h> #include <unistd.h> #include <signal.h> #include <alloca.h> 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 <aa>: 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 <aa+0x24>,r0 This patch fixes the bug by truncating the "frame" variable to 32 bits. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Cc: stable@vger.kernel.org --- arch/parisc/kernel/signal.c | 5 +++++ 1 file changed, 5 insertions(+)