From: Mark Rutland <mark.rutland@xxxxxxx>
commit f5d71291841aecfe5d8435da2dfa7f58ccd18bc8 upstream.
Currently fpmr_set() doesn't initialize the temporary 'fpmr' variable,
and a SETREGSET call with a length of zero will leave this
uninitialized. Consequently an arbitrary value will be written back to
target->thread.uw.fpmr, potentially leaking up to 64 bits of memory from
the kernel stack. The read is limited to a specific slot on the stack,
and the issue does not provide a write mechanism.
Fix this by initializing the temporary value before copying the regset
from userspace, as for other regsets (e.g. NT_PRSTATUS, NT_PRFPREG,
NT_ARM_SYSTEM_CALL). In the case of a zero-length write, the existing
contents of FPMR will be retained.
Before this patch:
| # ./fpmr-test
| Attempting to write NT_ARM_FPMR::fpmr = 0x900d900d900d900d
| SETREGSET(nt=0x40e, len=8) wrote 8 bytes
|
| Attempting to read NT_ARM_FPMR::fpmr
| GETREGSET(nt=0x40e, len=8) read 8 bytes
| Read NT_ARM_FPMR::fpmr = 0x900d900d900d900d
|
| Attempting to write NT_ARM_FPMR (zero length)
| SETREGSET(nt=0x40e, len=0) wrote 0 bytes
|
| Attempting to read NT_ARM_FPMR::fpmr
| GETREGSET(nt=0x40e, len=8) read 8 bytes
| Read NT_ARM_FPMR::fpmr = 0xffff800083963d50
After this patch:
| # ./fpmr-test
| Attempting to write NT_ARM_FPMR::fpmr = 0x900d900d900d900d
| SETREGSET(nt=0x40e, len=8) wrote 8 bytes
|
| Attempting to read NT_ARM_FPMR::fpmr
| GETREGSET(nt=0x40e, len=8) read 8 bytes
| Read NT_ARM_FPMR::fpmr = 0x900d900d900d900d
|
| Attempting to write NT_ARM_FPMR (zero length)
| SETREGSET(nt=0x40e, len=0) wrote 0 bytes
|
| Attempting to read NT_ARM_FPMR::fpmr
| GETREGSET(nt=0x40e, len=8) read 8 bytes
| Read NT_ARM_FPMR::fpmr = 0x900d900d900d900d
Fixes: 4035c22ef7d4 ("arm64/ptrace: Expose FPMR via ptrace")
Cc: <stable@xxxxxxxxxxxxxxx> # 6.9.x
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Reviewed-by: Mark Brown <broonie@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20241205121655.1824269-3-mark.rutland@xxxxxxx
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/kernel/ptrace.c | 2 ++
1 file changed, 2 insertions(+)
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -719,6 +719,8 @@ static int fpmr_set(struct task_struct *
if (!system_supports_fpmr())
return -EINVAL;
+ fpmr = target->thread.uw.fpmr;
+
ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &fpmr, 0, count);
if (ret)
return ret;
Patches currently in stable-queue which might be from mark.rutland@xxxxxxx are
queue-6.12/arm64-ptrace-fix-partial-setregset-for-nt_arm_fpmr.patch
queue-6.12/arm64-ptrace-fix-partial-setregset-for-nt_arm_tagged_addr_ctrl.patch
queue-6.12/arm64-ptrace-fix-partial-setregset-for-nt_arm_poe.patch
queue-6.12/arm64-ensure-bits-asid-are-masked-out-when-the-kernel-uses-8-bit-asids.patch
