On Tue, Apr 30, 2024 at 10:37:59AM +0200, Alexandre Ghiti wrote: > Hi Joel, Nam, > > On 30/04/2024 09:31, Nam Cao wrote: > > On Mon, Apr 29, 2024 at 02:52:30PM +0200, Joel Granados wrote: > >> On Thu, Apr 18, 2024 at 12:29:43PM +0200, 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. > >>> > >>> 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: ) > >>> > >>> 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. > >>> > >>> 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. > >>> > >>> 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. > >>> > >>> 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. > >>> > >>> Closes: https://lore.kernel.org/linux-riscv/878r1ibpdn.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx > >>> Signed-off-by: Nam Cao <namcao@xxxxxxxxxxxxx> > >>> Cc: <stable@xxxxxxxxxxxxxxx> # all versions > >>> --- > >>> init/main.c | 1 + > >>> 1 file changed, 1 insertion(+) > >>> > >>> diff --git a/init/main.c b/init/main.c > >>> index 881f6230ee59..f8d2793c4641 100644 > >>> --- a/init/main.c > >>> +++ b/init/main.c > >>> @@ -900,6 +900,7 @@ void start_kernel(void) > >>> page_address_init(); > >>> pr_notice("%s", linux_banner); > >>> early_security_init(); > >>> + memblock_reserve(__pa(-PAGE_SIZE), PAGE_SIZE); /* reserve last page for ERR_PTR */ > >>> setup_arch(&command_line); > >>> setup_boot_config(); > >>> setup_command_line(command_line); > >>> -- > >>> 2.39.2 > >>> > >> I received a similar(ish) report recently > >> https://lore.kernel.org/oe-kbuild-all/202404211031.J6l2AfJk-lkp@xxxxxxxxx/ > >> regarding RISC-V in init/mail.c. Here is the meat of the report in case > >> you want to avoid going to the actual link: > > This issue doesn't look like it has anything to do with this patch: this > > patch is about overlapping of dynamically allocated memory, while I think > > the issue is about overlapping sections during linking (maybe something > > wrong with riscv linker script?) > > > > Also, FWIW, this patch is not going to be in mainline because of a > > regression. > > > > Nonetheless, I will have a look at this later. > > > The config shows that it is a XIP kernel that comes with its own > limitations (text is limited to 32MB for example), so I'm not surprised > to see those overlaps. > > We already discussed the removal of randconfig builds on XIP configs, > but IIRC it is not possible. I just tested this going back until "2023-09-20 602bf1830798 (HEAD) Merge branch 'for-6.7' into for-next [Petr Mladek]" and I still saw the overlapping errors. Is this just something that happens always? Best -- Joel Granados
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