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Wed, 04 Nov 2026 02:45:47 -0800 (PST) Received: from pve-server ([49.205.216.49]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-36ca362f38asm7670687eec.0.2026.11.04.02.45.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2026 02:45:46 -0800 (PST) From: Ritesh Harjani (IBM) To: "Christophe Leroy (CS GROUP)" , linuxppc-dev@lists.ozlabs.org Cc: Madhavan Srinivasan , Venkat Rao Bagalkote , linux-kernel@vger.kernel.org, Michael Ellerman , Nicholas Piggin , Hari Bathini , stable@vger.kernel.org, Josef Schlehofer Subject: Re: [PATCH] powerpc/code-patching: Flush the patch area TLB entry locally In-Reply-To: Date: Wed, 04 Nov 2026 16:07:08 +0530 Message-ID: References: <44406eef-0035-4d6f-a2b0-3647d7c1ea2e@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-version: 1.0 Content-type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit "Christophe Leroy (CS GROUP)" writes: > Le 03/11/2026 à 10:12, Ritesh Harjani a écrit : >> "Christophe Leroy (CS GROUP)" writes: >> >>> Le 03/11/2026 à 03:54, Ritesh Harjani (IBM) a écrit : >>>> patching functions like patch_mem() and patch_instructions(), maps the >>>> target page at the per-cpu text_poke_area, write it, clear the PTE and >>>> then flushes the tlb using flush_tlb_kernel_range(), with interrupts >>>> disabled. flush_tlb_kernel_range() on SMP nohash (e500) does an IPI >>>> based TLB invalidation i.e - >>>> >>>> smp_call_function(do_flush_tlb_mm_ipi, NULL, 1); >>>> >>>> ...which will wait for other CPUs but with interrupts off. This can be >>>> caught by lockdep with the following warning: >>>> >>>> WARNING: kernel/smp.c:917 at smp_call_function_many_cond+0x430/0x818, CPU#1: swapper/0/1 >>>> CPU: 1 UID: 0 PID: 1 Comm: swapper/0 Not tainted 7.3.0-rc1-leds-v4 #1 PREEMPT >>>> Hardware name: Turris 1.1 e500v2 0x80211051 Freescale P2020 >>>> Call Trace: >>>> [c1915bc0] [c001be04] flush_tlb_kernel_range+0x2c/0x74 >>>> [c1915bd0] [c001ce2c] patch_instructions+0x1b0/0x318 >>>> [c1915c20] [c003113c] bpf_arch_text_copy+0x5c/0xb4 >>>> [c1915c40] [c01c3398] bpf_jit_binary_pack_finalize+0x28/0x8c >>>> [c1915c60] [c0031770] bpf_int_jit_compile+0x5dc/0x758 >>>> ... >>>> [c1915dd0] [c102e114] ptp_classifier_init+0x30/0x4c >>>> [c1915df0] [c102d3a8] sock_init+0xc8/0xe4 >>>> ... >>>> hardirqs last disabled at (3076): [] patch_instructions+0x238/0x318 >>>> >>>> Josef confirmed that this was causing a hang (deadlock): >>>> I think this is why the CZ.NIC Turris 1.1 hangs early in boot with >>>> CONFIG_JUMP_LABEL=y. On 6.18.44 it hung in 19 of 19 boots and booted >>>> fine 9 of 9 times with jump labels off. The hang comes while static >>>> keys are patched and modules are loaded, nothing is printed and the >>>> watchdog resets the board. OpenWrt keeps jump labels off on these >>>> boards for now. >>>> >>>> ...which is possible if both cpus are doing similar operations with interrupts >>>> off and doing TLB invalidation using IPI. >>>> >>>> Broadcast TLB invalidation is not needed here since text_poke_area is >>>> a per-cpu area. It is mapped and unmapped with interrupts disabled by >>>> it's own cpu. The only reason I think, if we would need a broadcast tlb >>>> invalidate is, when we want to prevent a stray or malicious write to >>>> this cpu text_poke_area by another CPU. This generally gets solved with >>>> temporary-mm path like how Radix and even x86 implements. However, booke >>>> doesn't implement that, so for now let's ensure we use local tlb >>>> flushing for correctness. >>> >>> This problem was already discussed one year ago, see >>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2FPA3P192MB2865C07D634E3B775D003C7F8CD7A%40PA3P192MB2865.EURP192.PROD.OUTLOOK.COM%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C94ba9bffb5d647f9790208df398f6ccb%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639292960305489629%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=RgVxRJOlFSWgNsFSKwLDRinx3kaF4LpSiCaTey8xtic%3D&reserved=0 >>> >>> See response from Arnd, a stop_machine() should be done for completeness. >>> >> >> I will have to take sometime to go over what ARM does here with >> stop_machine(). However, either ways I think, we still need this fix, >> since otherwise P2020 boards gets hung during boot. Thoughts? > > That's right, it must be fixed. The global TLB flush must likely be > changed to a local TLB flush, but that's not enough to get a safe system. > Ok then, will spend sometime looking at how other archs handles this. Although IIUC - even with TLB invalidation using IPI there is a window where the remote cpu could use a stale tlb. But the window is too small, however, with only local tlb invalidate, if in case the remote cpu has a stale TLB, it will never get flushed. >> >> >>>> >>>> Fixes: 49e3d8ea6248 ("powerpc/fsl_booke: Enable STRICT_KERNEL_RWX") >>>> Cc: stable@vger.kernel.org >>>> Reported-by: Josef Schlehofer >>>> Closes: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F20261026195644.16384-1-pepe.schlehofer%40gmail.com%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C94ba9bffb5d647f9790208df398f6ccb%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639292960305519321%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=A50lEHBZBaX70jGTu38GylmnQvlxVzLalMVXYj2kti0%3D&reserved=0 >>>> Tested-by: Josef Schlehofer >>>> Signed-off-by: Ritesh Harjani (IBM) >>>> --- >>>> arch/powerpc/lib/code-patching.c | 21 +++++++++++++++++++-- >>>> 1 file changed, 19 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c >>>> index 44ff9f684bef..6351342fa5c3 100644 >>>> --- a/arch/powerpc/lib/code-patching.c >>>> +++ b/arch/powerpc/lib/code-patching.c >>>> @@ -276,6 +276,23 @@ static int __do_patch_mem_mm(void *addr, unsigned long val, bool is_dword) >>>> return err; >>>> } >>>> >>>> +/* >>>> + * The patch area is per-CPU and only used by its own CPU, with IRQs >>>> + * disabled, so only the local TLB can hold an entry for it. >>>> + * >>>> + * On nohash SMP, flush_tlb_kernel_range() IPIs the other CPUs and waits, which >>>> + * must not be done with IRQs disabled (see smp_call_function_many_cond()), so >>>> + * flush just the local kernel (PID 0) entry. >>>> + * Book3S keeps flush_tlb_kernel_range() which doesn't IPI here. >>>> + */ >>>> +static void flush_patch_area(unsigned long addr) >>>> +{ >>>> + if (IS_ENABLED(CONFIG_PPC_BOOK3S)) >>> >>> CONFIG_PPC_BOOK3S not consistant with commit message. Are you adressing >>> a problem on e500 only ? on all not book3s ? What about book3s/32 ? What >>> about 8xx ? Even for book3s/64, is it correct at all when >>> mm_patch_enabled() returns false ? >>> >> >> No we are addressing the problem on all NOHASH platforms. IIUC, all >> !BOOK3S are "nohash". Although some of them maybe UP, so it doesn't >> matter whether a flush_tlb_kernel_range() is called or >> local_flush_tlb_page() - it wouldn't matter. And on others which are SMP >> but do not have STRICT_KERNEL_RWX enabled, they will anyway not go >> through this path - but if they ever do - then we should ensure they too >> do a local_flush_tlb_range() to avoid the same deadlock. >> >> However, I think, maybe we could use CONFIG_PPC_MMU_NOHASH instead of using >> CONFIG_PPC_BOOK3S, thoughts? > > Well they are equivalent, so it doesn't solve the issue I think: > > config PPC_MMU_NOHASH > def_bool y > depends on !PPC_BOOK3S > > What about book3s/64 in hash mode ? What about book3s/32 ? None of them > implement temporary_mm, so are they covered ? > They both use TLBIE (global/broadcast TLB invalidation). With that we don't need to use IPI for TLB invalidation. > Christophe > Thanks for the review comments. Let me check on the stop_machine() or other alternative to fix the security gap as well. At the moment, I have my hands full with couple of other things, but hopefully I can come back on this once they are somewhat taken care of. -ritesh >> >> >> -ritesh >> >>>> + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); >>>> + else >>>> + local_flush_tlb_page(NULL, addr); >>>> +} >>>> + >>>> static int __do_patch_mem(void *addr, unsigned long val, bool is_dword) >>>> { >>>> int err; >>>> @@ -296,7 +313,7 @@ static int __do_patch_mem(void *addr, unsigned long val, bool is_dword) >>>> err = __patch_mem(addr, val, patch_addr, is_dword); >>>> >>>> pte_clear(&init_mm, text_poke_addr, pte); >>>> - flush_tlb_kernel_range(text_poke_addr, text_poke_addr + PAGE_SIZE); >>>> + flush_patch_area(text_poke_addr); >>>> >>>> return err; >>>> } >>>> @@ -488,7 +505,7 @@ static int __do_patch_instructions(u32 *addr, u32 *code, size_t len, bool repeat >>>> err = __patch_instructions(patch_addr, code, len, repeat_instr); >>>> >>>> pte_clear(&init_mm, text_poke_addr, pte); >>>> - flush_tlb_kernel_range(text_poke_addr, text_poke_addr + PAGE_SIZE); >>>> + flush_patch_area(text_poke_addr); >>>> >>>> return err; >>>> } >>>> -- >>>> 2.39.5 >>>>