From: Mark Brown broonie@kernel.org
mainline inclusion from mainline-v6.5-rc3 commit d4d5be94a87872421ea2569044092535aff0b886 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I8E73O CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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When we reconfigure the SVE vector length we discard the backing storage for the SVE vectors and then reallocate on next SVE use, leaving the SME specific state alone. This means that we do not enable SME traps if they were already disabled. That means that userspace code can enter streaming mode without trapping, putting the task in a state where if we try to save the state of the task we will fault.
Since the ABI does not specify that changing the SVE vector length disturbs SME state, and since SVE code may not be aware of SME code in the process, we shouldn't simply discard any ZA state. Instead immediately reallocate the storage for SVE, and disable SME if we change the SVE vector length while there is no SME state active.
Disabling SME traps on SVE vector length changes would make the overall code more complex since we would have a state where we have valid SME state stored but might get a SME trap.
Fixes: 9e4ab6c89109 ("arm64/sme: Implement vector length configuration prctl()s") Reported-by: David Spickett David.Spickett@arm.com Signed-off-by: Mark Brown broonie@kernel.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20230720-arm64-fix-sve-sme-vl-change-v2-1-8eea06b8... Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Wang ShaoBo bobo.shaobowang@huawei.com --- arch/arm64/kernel/fpsimd.c | 33 +++++++++++++++++++++++++-------- 1 file changed, 25 insertions(+), 8 deletions(-)
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 49fa50a09d4b6..cf76f1d6b1a7b 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -781,6 +781,8 @@ void sve_sync_from_fpsimd_zeropad(struct task_struct *task) int vec_set_vector_length(struct task_struct *task, enum vec_type type, unsigned long vl, unsigned long flags) { + bool free_sme = false; + if (flags & ~(unsigned long)(PR_SVE_VL_INHERIT | PR_SVE_SET_VL_ONEXEC)) return -EINVAL; @@ -829,21 +831,36 @@ int vec_set_vector_length(struct task_struct *task, enum vec_type type, thread_sm_enabled(&task->thread)) sve_to_fpsimd(task);
- if (system_supports_sme() && type == ARM64_VEC_SME) { - task->thread.svcr &= ~(SVCR_SM_MASK | - SVCR_ZA_MASK); - clear_thread_flag(TIF_SME); + if (system_supports_sme()) { + if (type == ARM64_VEC_SME || + !(task->thread.svcr & (SVCR_SM_MASK | SVCR_ZA_MASK))) { + /* + * We are changing the SME VL or weren't using + * SME anyway, discard the state and force a + * reallocation. + */ + task->thread.svcr &= ~(SVCR_SM_MASK | + SVCR_ZA_MASK); + clear_thread_flag(TIF_SME); + free_sme = true; + } }
if (task == current) put_cpu_fpsimd_context();
/* - * Force reallocation of task SVE and SME state to the correct - * size on next use: + * Free the changed states if they are not in use, SME will be + * reallocated to the correct size on next use and we just + * allocate SVE now in case it is needed for use in streaming + * mode. */ - sve_free(task); - if (system_supports_sme() && type == ARM64_VEC_SME) + if (system_supports_sve()) { + sve_free(task); + sve_alloc(task, true); + } + + if (free_sme) sme_free(task);
task_set_vl(task, type, vl);