FAILED: patch "[PATCH] powerpc: Don't try to copy PPR for task with NULL pt_regs" failed to apply to 5.4-stable tree

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 <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x fd7276189450110ed835eb0a334e62d2f1c4e3be
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023040302-flakily-define-371e@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

fd7276189450 ("powerpc: Don't try to copy PPR for task with NULL pt_regs") 47e12855a91d ("powerpc: switch to ->regset_get()")
6e0b79750ce2 ("powerpc/ptrace: move register viewing functions out of ptrace.c") 7c1f8db019f8 ("powerpc/ptrace: split out TRANSACTIONAL_MEM related functions.") 60ef9dbd9d2a ("powerpc/ptrace: split out SPE related functions.") 1b20773b00b7 ("powerpc/ptrace: split out ALTIVEC related functions.") 7b99ed4e8e3a ("powerpc/ptrace: split out VSX related functions.") 963ae6b2ff1c ("powerpc/ptrace: drop PARAMETER_SAVE_AREA_OFFSET") f1763e623c69 ("powerpc/ptrace: drop unnecessary #ifdefs CONFIG_PPC64") b3138536c837 ("powerpc/ptrace: remove unused header includes") da9a1c10e2c7 ("powerpc: Move ptrace into a subdirectory.") 68b34588e202 ("powerpc/64/sycall: Implement syscall entry/exit logic in C") 965dd3ad3076 ("powerpc/64/syscall: Remove non-volatile GPR save optimisation") fddb5d430ad9 ("open: introduce openat2(2) syscall")
793b08e2efff ("powerpc/kexec: Move kexec files into a dedicated subdir.") 9f7bd9201521 ("powerpc/32: Split kexec low level code out of misc_32.S") b020aa9d1e87 ("powerpc: cleanup hw_irq.h")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From fd7276189450110ed835eb0a334e62d2f1c4e3be Mon Sep 17 00:00:00 2001
From: Jens Axboe <[email protected]>
Date: Sun, 26 Mar 2023 16:15:57 -0600
Subject: [PATCH] powerpc: Don't try to copy PPR for task with NULL pt_regs

powerpc sets up PF_KTHREAD and PF_IO_WORKER with a NULL pt_regs, which from my (arguably very short) checking is not commonly done for other archs. This is fine, except when PF_IO_WORKER's have been created and the task does something that causes a coredump to be generated. Then we get this crash:

Kernel attempted to read user page (160) - exploit attempt? (uid: 1000)

  BUG: Kernel NULL pointer dereference on read at 0x00000160
  Faulting instruction address: 0xc0000000000c3a60
  Oops: Kernel access of bad area, sig: 11 [#1]
  LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=32 NUMA pSeries
  Modules linked in: bochs drm_vram_helper drm_kms_helper xts binfmt_misc ecb ctr syscopyarea sysfillrect cbc sysimgblt drm_ttm_helper aes_generic ttm sg libaes evdev joydev virtio_balloon vmx_crypto gf128mul drm dm_mod fuse loop configfs drm_panel_orientation_quirks ip_tables x_tables autofs4 hid_generic usbhid hid xhci_pci xhci_hcd usbcore usb_common sd_mod
  CPU: 1 PID: 1982 Comm: ppc-crash Not tainted 6.3.0-rc2+ #88
  Hardware name: IBM pSeries (emulated by qemu) POWER9 (raw) 0x4e1202 0xf000005 of:SLOF,HEAD hv:linux,kvm pSeries
  NIP:  c0000000000c3a60 LR: c000000000039944 CTR: c0000000000398e0
  REGS: c0000000041833b0 TRAP: 0300   Not tainted  (6.3.0-rc2+)
  MSR:  800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 88082828  XER: 200400f8
  ...
  NIP memcpy_power7+0x200/0x7d0
  LR  ppr_get+0x64/0xb0
  Call Trace:
    ppr_get+0x40/0xb0 (unreliable)
    __regset_get+0x180/0x1f0
    regset_get_alloc+0x64/0x90
    elf_core_dump+0xb98/0x1b60
    do_coredump+0x1c34/0x24a0
    get_signal+0x71c/0x1410
    do_notify_resume+0x140/0x6f0
    interrupt_exit_user_prepare_main+0x29c/0x320
    interrupt_exit_user_prepare+0x6c/0xa0
    interrupt_return_srr_user+0x8/0x138

Because ppr_get() is trying to copy from a PF_IO_WORKER with a NULL pt_regs.

Check for a valid pt_regs in both ppc_get/ppr_set, and return an error if not set. The actual error value doesn't seem to be important here, so just pick -EINVAL.

index 2087a785f05f..5fff0d04b23f 100644
@@ -290,6 +290,9 @@ static int gpr_set(struct task_struct *target, const struct user_regset *regset,
 static int ppr_get(struct task_struct *target, const struct user_regset *regset,
 		   struct membuf to)
 {
+	if (!target->thread.regs)
+		return -EINVAL;
+
 	return membuf_write(&to, &target->thread.regs->ppr, sizeof(u64));
 }
 

@@ -297,6 +300,9 @@ static int ppr_set(struct task_struct *target, const struct user_regset *regset,
 		   unsigned int pos, unsigned int count, const void *kbuf,
 		   const void __user *ubuf)
 {
+	if (!target->thread.regs)
+		return -EINVAL;
+
 	return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
 				  &target->thread.regs->ppr, 0, sizeof(u64));
 }

PF_IO_WORKER doesn't exist before 5.10-stable, so we don't need to backport this patch to older version. You can drop this one, and the ones for 4.x.

Jens Axboe

Great, thanks for letting us know.

greg k-h