Messages in this thread | | | From | Heiko Stuebner <> | Subject | Re: [PATCH 1/2] riscv: prevent null-pointer dereference with sbi_remote_fence_i | Date | Tue, 14 Dec 2021 11:41:48 +0100 |
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Hi Atish,
Am Dienstag, 14. Dezember 2021, 02:51:17 CET schrieb Atish Patra: > On Mon, Dec 13, 2021 at 3:21 AM Heiko Stuebner <heiko@sntech.de> wrote: > > > > The callback used inside sbi_remote_fence_i is set at sbi probe time > > to the needed variant. Before that it is a NULL pointer. > > > > The selection between using sbi_remote_fence_i or ipi_remote_fence_i > > right now is solely done on the presence of the RISCV_SBI config option. > > > > On a multiplatform kernel, SBI will probably always be built in, but > > in the future not all machines using that kernel may have SBI > > on them, so in some cases this setup can lead to NULL pointer dereferences. > > > > I didn't quite understand this. The only platforms without SBI are > M-mode Linux based platforms. > All other platforms will require SBI if the kernel is running on > supervisor mode.
Ok ... but imagine a single-core board starting in S-mode. Not doing smp, kvm, etc.
So I can very well imagine the possibility that people might start it without an sbi instance running ;-) .
> They may not need SBI IPI or SBI RFENCE extensions if an alternate > mechanism(ACLINT SSWI or AIA IMSIC) > is already available in hardware. IIRC, Anup's aclint & aia series > already takes care of that. > > > Also if in future one of the flush_icache_all / flush_icache_mm functions > > gets called earlier in the boot process - before sbi_init - this would > > trigger the issue. > > > > sbi_init is called before setup_smp. Do you think there is a use case where > flush_icache_xxx can be called before smp initialization ?
I ran into the issue while experimenting with doing alternatives patching earlier. Works fine, but the flush_icache call then runs into that null-ptr.
Heiko
> > To prevent this, add a default __sbi_rfence_none returning an error code > > and adapt the callers to check for an error from the remote fence > > to then fall back to the other method. > > > > Having said that, it is always good to have guards to avoid NULL > pointer dereferences. > However, the commit text may be updated based on the above questions. > > > Signed-off-by: Heiko Stuebner <heiko@sntech.de> > > --- > > arch/riscv/kernel/sbi.c | 10 +++++++++- > > arch/riscv/mm/cacheflush.c | 25 +++++++++++++++++-------- > > 2 files changed, 26 insertions(+), 9 deletions(-) > > > > diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c > > index 7402a417f38e..69d0a96b97d0 100644 > > --- a/arch/riscv/kernel/sbi.c > > +++ b/arch/riscv/kernel/sbi.c > > @@ -14,11 +14,19 @@ > > unsigned long sbi_spec_version __ro_after_init = SBI_SPEC_VERSION_DEFAULT; > > EXPORT_SYMBOL(sbi_spec_version); > > > > +static int __sbi_rfence_none(int fid, const unsigned long *hart_mask, > > + unsigned long start, unsigned long size, > > + unsigned long arg4, unsigned long arg5) > > +{ > > + return -EOPNOTSUPP; > > +} > > + > > static void (*__sbi_set_timer)(uint64_t stime) __ro_after_init; > > static int (*__sbi_send_ipi)(const unsigned long *hart_mask) __ro_after_init; > > static int (*__sbi_rfence)(int fid, const unsigned long *hart_mask, > > unsigned long start, unsigned long size, > > - unsigned long arg4, unsigned long arg5) __ro_after_init; > > + unsigned long arg4, unsigned long arg5) > > + __ro_after_init = __sbi_rfence_none; > > > > struct sbiret sbi_ecall(int ext, int fid, unsigned long arg0, > > unsigned long arg1, unsigned long arg2, > > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c > > index 89f81067e09e..128e23c094ea 100644 > > --- a/arch/riscv/mm/cacheflush.c > > +++ b/arch/riscv/mm/cacheflush.c > > @@ -16,11 +16,15 @@ static void ipi_remote_fence_i(void *info) > > > > void flush_icache_all(void) > > { > > + int ret = -EINVAL; > > + > > local_flush_icache_all(); > > > > if (IS_ENABLED(CONFIG_RISCV_SBI)) > > - sbi_remote_fence_i(NULL); > > - else > > + ret = sbi_remote_fence_i(NULL); > > + > > + /* fall back to ipi_remote_fence_i if sbi failed or not available */ > > + if (ret) > > on_each_cpu(ipi_remote_fence_i, NULL, 1); > > } > > EXPORT_SYMBOL(flush_icache_all); > > @@ -66,13 +70,18 @@ void flush_icache_mm(struct mm_struct *mm, bool local) > > * with flush_icache_deferred(). > > */ > > smp_mb(); > > - } else if (IS_ENABLED(CONFIG_RISCV_SBI)) { > > - cpumask_t hartid_mask; > > - > > - riscv_cpuid_to_hartid_mask(&others, &hartid_mask); > > - sbi_remote_fence_i(cpumask_bits(&hartid_mask)); > > } else { > > - on_each_cpu_mask(&others, ipi_remote_fence_i, NULL, 1); > > + int ret = -EINVAL; > > + > > + if (IS_ENABLED(CONFIG_RISCV_SBI)) { > > + cpumask_t hartid_mask; > > + > > + riscv_cpuid_to_hartid_mask(&others, &hartid_mask); > > + ret = sbi_remote_fence_i(cpumask_bits(&hartid_mask)); > > This API is removed in sparse hartid series[1]. You may want to rebase > on top of it. > > [1] https://patchwork.kernel.org/project/linux-riscv/list/?series=590195 > > > + } > > + > > + if (ret) > > + on_each_cpu_mask(&others, ipi_remote_fence_i, NULL, 1); > > } > > > > preempt_enable(); > > -- > > 2.30.2 > > > > > > _______________________________________________ > > linux-riscv mailing list > > linux-riscv@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-riscv > > > >
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