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 Nvfx+Wf1 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vmalloc() and later expanded with > > vrealloc() — while still within the originally allocated size — > > KASAN may report a false positive because > > it does not update the tags for the newly expanded portion of the memory. > > > > A typical example of this pattern occurs in the BPF verifier, > > and the following is a related false positive report: > > > > [ 2206.486476] ================================================================== > > [ 2206.486509] BUG: KASAN: invalid-access in __memcpy+0xc/0x30 > > [ 2206.486607] Write at addr f5ff800083765270 by task test_progs/205 > > [ 2206.486664] Pointer tag: [f5], memory tag: [fe] > > [ 2206.486703] > > [ 2206.486745] CPU: 4 UID: 0 PID: 205 Comm: test_progs Tainted: G OE 6.18.0-rc7+ #145 PREEMPT(full) > > [ 2206.486861] Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE > > [ 2206.486897] Hardware name: , BIOS > > [ 2206.486932] Call trace: > > [ 2206.486961] show_stack+0x24/0x40 (C) > > [ 2206.487071] __dump_stack+0x28/0x48 > > [ 2206.487182] dump_stack_lvl+0x7c/0xb0 > > [ 2206.487293] print_address_description+0x80/0x270 > > [ 2206.487403] print_report+0x94/0x100 > > [ 2206.487505] kasan_report+0xd8/0x150 > > [ 2206.487606] __do_kernel_fault+0x64/0x268 > > [ 2206.487717] do_bad_area+0x38/0x110 > > [ 2206.487820] do_tag_check_fault+0x38/0x60 > > [ 2206.487936] do_mem_abort+0x48/0xc8 > > [ 2206.488042] el1_abort+0x40/0x70 > > [ 2206.488127] el1h_64_sync_handler+0x50/0x118 > > [ 2206.488217] el1h_64_sync+0xa4/0xa8 > > [ 2206.488303] __memcpy+0xc/0x30 (P) > > [ 2206.488412] do_misc_fixups+0x4f8/0x1950 > > [ 2206.488528] bpf_check+0x31c/0x840 > > [ 2206.488638] bpf_prog_load+0x58c/0x658 > > [ 2206.488737] __sys_bpf+0x364/0x488 > > [ 2206.488833] __arm64_sys_bpf+0x30/0x58 > > [ 2206.488920] invoke_syscall+0x68/0xe8 > > [ 2206.489033] el0_svc_common+0xb0/0xf8 > > [ 2206.489143] do_el0_svc+0x28/0x48 > > [ 2206.489249] el0_svc+0x40/0xe8 > > [ 2206.489337] el0t_64_sync_handler+0x84/0x140 > > [ 2206.489427] el0t_64_sync+0x1bc/0x1c0 > > > > Here, 0xf5ff800083765000 is vmalloc()ed address for > > env->insn_aux_data with the size of 0x268. > > While this region is expanded size by 0x478 and initialise > > increased region to apply patched instructions, > > a false positive is triggered at the address 0xf5ff800083765270 > > because __kasan_unpoison_vmalloc() with KASAN_VMALLOC_PROT_NORMAL flag only > > doesn't update the tag on increaed region. > > > > To address this, introduces KASAN_VMALLOC_EXPAND flag which > > is used to expand vmalloc()ed memory in range of real allocated size > > to update tag for increased region. > > Thanks. > > > Fixes: 23689e91fb22 ("kasan, vmalloc: add vmalloc tagging for HW_TAGS”) > > Cc: > > Unfortunately this is changing the same code as "mm/kasan: fix > incorrect unpoisoning in vrealloc for KASAN", > (https://lkml.kernel.org/r/20251128111516.244497-1-jiayuan.chen@linux.dev) > which is also cc:stable. > > So could you please take a look at the code in mm.git's > mm-hotfixes-unstable branch > (git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm) and base the > fix upon that? This way everything should merge and backport nicely. Thanks for sharing this :) But I think the patch from Jiayuan still has a problem since vrealloc() can pass the "unaligned address" with KASAN_GRANULE_SIZE and this will trigger WARN_ON() in kasan_unpoison(). Except that I don't have a strong opinion whether adding a new interface or a new flag. But, I want to receive a comment from KASAN maintainers to check what is better. -- Sincerely, Yeoreum Yun