[PATCH 2/4] arm64: ptrace: fix partial SETREGSET for NT_ARM_FPMR
Mark Rutland
mark.rutland at arm.com
Thu Dec 5 04:16:53 PST 2024
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: 4035c22ef7d43a6c ("arm64/ptrace: Expose FPMR via ptrace")
Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Mark Brown <broonie at kernel.org>
Cc: Will Deacon <will at kernel.org>
---
arch/arm64/kernel/ptrace.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 8525d03f0fb40..85c862dc845b3 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -720,6 +720,8 @@ static int fpmr_set(struct task_struct *target, const struct user_regset *regset
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;
--
2.30.2
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