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15:01:48 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1713445310; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=0GJg4wo0VKLac1PG97GL83QKeqaA9szY5zPKromLH+A=; b=td7NRfGfcrv0MyyqY+R9o3SoF/k2jyFG+Hw7c1iUg6sGEx/jr18/rj4iS1DJnfvGCR68pw rPRsi11sW51RYh1zIYoVxRPbgMoAcCiEAMrRLR9nlGI5MXoHvXTg5w8haFnEipTHC8L2HL GWVwjcdQbvWzbsxenfbbEpLyISg/ZtzSzQqBBJIKiBRu1NpOfgm0acuuLOqhmM7RBrjlCv s1DWtTp64zduTiWs856+1dllq2b+ovcJwOPy67hRL8w+Lhx9oDOQqbijAjb1461hu1NJiM A0X0DzUjidKOd+p1q3gRJpZoCjKF40N02qN+mT8SxrMv/j+9pK+Fqj7LhvA3Yw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1713445310; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=0GJg4wo0VKLac1PG97GL83QKeqaA9szY5zPKromLH+A=; b=NTafIBCYsXh1Tdh3iOhsXmxdqRGVtfe43CHFbsPqgsih4/iAHkX8D+I5XsL1Gc1tYxHC6+ BnB4ua0EWdlKKbCw== From: Nam Cao To: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= Cc: Mike Rapoport , Andreas Dilger , linux-riscv@lists.infradead.org, Thomas Gleixner , Andrew Morton , "ndesaulniers @ google . com" , Luis Chamberlain , Ingo Molnar , Christophe Leroy , Tejun Heo , Krister Johansen , Changbin Du , Arnd Bergmann , Geert Uytterhoeven , linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] init: fix allocated page overlapping with PTR_ERR Message-ID: <20240418150148.6a0b4664@namcao> In-Reply-To: <87edb2sv0d.fsf@all.your.base.are.belong.to.us> References: <20240418102943.180510-1-namcao@linutronix.de> <20240418131238.636bee2c@namcao> <87edb2sv0d.fsf@all.your.base.are.belong.to.us> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 2024-04-18 Bj=C3=B6rn T=C3=B6pel wrote: > Nam Cao writes: >=20 > > On 2024-04-18 Nam Cao wrote: > >> There is nothing preventing kernel memory allocators from allocating a > >> page that overlaps with PTR_ERR(), except for architecture-specific > >> code that setup memblock. > >>=20 > >> It was discovered that RISCV architecture doesn't setup memblock > >> corectly, leading to a page overlapping with PTR_ERR() being allocated, > >> and subsequently crashing the kernel (link in Close: ) > >>=20 > >> The reported crash has nothing to do with PTR_ERR(): the last page > >> (at address 0xfffff000) being allocated leads to an unexpected > >> arithmetic overflow in ext4; but still, this page shouldn't be > >> allocated in the first place. > >>=20 > >> Because PTR_ERR() is an architecture-independent thing, we shouldn't > >> ask every single architecture to set this up. There may be other > >> architectures beside RISCV that have the same problem. > >>=20 > >> Fix this one and for all by reserving the physical memory page that > >> may be mapped to the last virtual memory page as part of low memory. > >>=20 > >> Unfortunately, this means if there is actual memory at this reserved > >> location, that memory will become inaccessible. However, if this page > >> is not reserved, it can only be accessed as high memory, so this > >> doesn't matter if high memory is not supported. Even if high memory is > >> supported, it is still only one page. > >>=20 > >> Closes: https://lore.kernel.org/linux-riscv/878r1ibpdn.fsf@all.your.ba= se.are.belong.to.us > >> Signed-off-by: Nam Cao > >> Cc: # all versions > > > > Sorry, forgot to add: > > Reported-by: Bj=C3=B6rn T=C3=B6pel >=20 > Hmm, can't we get rid of the whole check in arch/riscv/mm/init.c for > 32b? We can, but that depends on this patch. So my intention is to wait for this patch to be applied first, because I don't want to bother the maintainers with dependencies. > --8<-- > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c > index fe8e159394d8..1e91d5728887 100644 > --- a/arch/riscv/mm/init.c > +++ b/arch/riscv/mm/init.c > @@ -196,7 +196,6 @@ early_param("mem", early_mem); > static void __init setup_bootmem(void) > { > phys_addr_t vmlinux_end =3D __pa_symbol(&_end); > - phys_addr_t max_mapped_addr; > phys_addr_t phys_ram_end, vmlinux_start; > =20 > if (IS_ENABLED(CONFIG_XIP_KERNEL)) > @@ -234,21 +233,6 @@ static void __init setup_bootmem(void) > if (IS_ENABLED(CONFIG_64BIT)) > kernel_map.va_pa_offset =3D PAGE_OFFSET - phys_ram_base; > =20 > - /* > - * memblock allocator is not aware of the fact that last 4K bytes of > - * the addressable memory can not be mapped because of IS_ERR_VALUE > - * macro. Make sure that last 4k bytes are not usable by memblock > - * if end of dram is equal to maximum addressable memory. For 64-bit > - * kernel, this problem can't happen here as the end of the virtual > - * address space is occupied by the kernel mapping then this check must > - * be done as soon as the kernel mapping base address is determined. > - */ > - if (!IS_ENABLED(CONFIG_64BIT)) { > - max_mapped_addr =3D __pa(~(ulong)0); > - if (max_mapped_addr =3D=3D (phys_ram_end - 1)) > - memblock_set_current_limit(max_mapped_addr - 4096); > - } > - If you are going to send this, you can add: Reviewed-by: Nam Cao > min_low_pfn =3D PFN_UP(phys_ram_base); > max_low_pfn =3D max_pfn =3D PFN_DOWN(phys_ram_end); > high_memory =3D (void *)(__va(PFN_PHYS(max_low_pfn))); > --8<-- >=20 > Mike hints that's *not* the case > (https://lore.kernel.org/linux-riscv/ZiAkRMUfiPDUGPdL@kernel.org/). > memblock_reserve() should disallow allocation as well, no? He said it can't be removed if we set max_low_pfn instead of using memblock_reserve() If max_low_pfn() is used, then it can be removed: https://lore.kernel.org/linux-riscv/Zh6n-nvnQbL-0xss@kernel.org Best regards, Nam