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authorMark Rutland <mark.rutland@arm.com>2024-12-05 12:16:53 +0000
committerCatalin Marinas <catalin.marinas@arm.com>2024-12-05 18:04:06 +0000
commitf5d71291841aecfe5d8435da2dfa7f58ccd18bc8 (patch)
tree4a50466ba5d0bcc0350d5b719354891bab58f453
parentca62d90085f4af36de745883faab9f8a7cbb45d3 (diff)
arm64: ptrace: fix partial SETREGSET for NT_ARM_FPMR
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@vger.kernel.org> # 6.9.x Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Mark Brown <broonie@kernel.org> Cc: Will Deacon <will@kernel.org> Reviewed-by: Mark Brown <broonie@kernel.org> Link: https://lore.kernel.org/r/20241205121655.1824269-3-mark.rutland@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
-rw-r--r--arch/arm64/kernel/ptrace.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 8525d03f0fb4..85c862dc845b 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;