* Re: [PATCH] riscv: Fix vector state restore in rt_sigreturn()
[not found] <20240403072638.567446-1-bjorn@kernel.org>
@ 2024-12-04 4:45 ` Yangyu Chen
2024-12-04 15:42 ` Sasha Levin
1 sibling, 0 replies; 3+ messages in thread
From: Yangyu Chen @ 2024-12-04 4:45 UTC (permalink / raw)
To: Björn Töpel, Paul Walmsley, Palmer Dabbelt, Albert Ou,
Andy Chiu, linux-riscv
Cc: Björn Töpel, Conor Dooley, Heiko Stuebner, Vincent Chen,
Ben Dooks, Greentime Hu, Haorong Lu, Jerry Shih, Nick Knight,
linux-kernel, Vineet Gupta, Charlie Jenkins, Vineet Gupta, stable
I think this patch should also be backported to the v6.6 LTS tree.
Since it should recolonize as Fixes: 8ee0b41898 ("riscv: signal:
Add sigcontext save/restore for vector") and that commit first
appears since v6.5-rc1 and this patch land to master branch since
v6.9-rc3
Thanks,
Yangyu Chen
On 4/3/24 15:26, Björn Töpel wrote:
> From: Björn Töpel <bjorn@rivosinc.com>
> The RISC-V Vector specification states in "Appendix D: Calling
> Convention for Vector State" [1] that "Executing a system call causes
> all caller-saved vector registers (v0-v31, vl, vtype) and vstart to
> become unspecified.". In the RISC-V kernel this is called "discarding
> the vstate".
> Returning from a signal handler via the rt_sigreturn() syscall, vector
> discard is also performed. However, this is not an issue since the
> vector state should be restored from the sigcontext, and therefore not
> care about the vector discard.
> The "live state" is the actual vector register in the running context,
> and the "vstate" is the vector state of the task. A dirty live state,
> means that the vstate and live state are not in synch.
> When vectorized user_from_copy() was introduced, an bug sneaked in at
> the restoration code, related to the discard of the live state.
> An example when this go wrong:
> 1. A userland application is executing vector code
> 2. The application receives a signal, and the signal handler is
> entered.
> 3. The application returns from the signal handler, using the
> rt_sigreturn() syscall.
> 4. The live vector state is discarded upon entering the
> rt_sigreturn(), and the live state is marked as "dirty", indicating
> that the live state need to be synchronized with the current
> vstate.
> 5. rt_sigreturn() restores the vstate, except the Vector registers,
> from the sigcontext
> 6. rt_sigreturn() restores the Vector registers, from the sigcontext,
> and now the vectorized user_from_copy() is used. The dirty live
> state from the discard is saved to the vstate, making the vstate
> corrupt.
> 7. rt_sigreturn() returns to the application, which crashes due to
> corrupted vstate.
> Note that the vectorized user_from_copy() is invoked depending on the
> value of CONFIG_RISCV_ISA_V_UCOPY_THRESHOLD. Default is 768, which
> means that vlen has to be larger than 128b for this bug to trigger.
> The fix is simply to mark the live state as non-dirty/clean prior
> performing the vstate restore.
> Link: https://github.com/riscv/riscv-isa-manual/releases/download/riscv-isa-release-8abdb41-2024-03-26/unpriv-isa-asciidoc.pdf # [1]
> Reported-by: Charlie Jenkins <charlie@rivosinc.com>
> Reported-by: Vineet Gupta <vgupta@kernel.org>
> Fixes: c2a658d41924 ("riscv: lib: vectorize copy_to_user/copy_from_user")
> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
> ---
> arch/riscv/kernel/signal.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
> diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
> index 501e66debf69..5a2edd7f027e 100644
> --- a/arch/riscv/kernel/signal.c
> +++ b/arch/riscv/kernel/signal.c
> @@ -119,6 +119,13 @@ static long __restore_v_state(struct pt_regs *regs, void __user *sc_vec)
> struct __sc_riscv_v_state __user *state = sc_vec;
> void __user *datap;
> + /*
> + * Mark the vstate as clean prior performing the actual copy,
> + * to avoid getting the vstate incorrectly clobbered by the
> + * discarded vector state.
> + */
> + riscv_v_vstate_set_restore(current, regs);
> +
> /* Copy everything of __sc_riscv_v_state except datap. */
> err = __copy_from_user(¤t->thread.vstate, &state->v_state,
> offsetof(struct __riscv_v_ext_state, datap));
> @@ -133,13 +140,7 @@ static long __restore_v_state(struct pt_regs *regs, void __user *sc_vec)
> * Copy the whole vector content from user space datap. Use
> * copy_from_user to prevent information leak.
> */
> - err = copy_from_user(current->thread.vstate.datap, datap, riscv_v_vsize);
> - if (unlikely(err))
> - return err;
> -
> - riscv_v_vstate_set_restore(current, regs);
> -
> - return err;
> + return copy_from_user(current->thread.vstate.datap, datap, riscv_v_vsize);
> }
> #else
> #define save_v_state(task, regs) (0)
> base-commit: 7115ff4a8bfed3b9294bad2e111744e6abeadf1a
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