| Message ID | a411788081d50e3b136c6270471e35aba3dfafa3.1729271995.git.ritesh.list@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | powerpc/kfence: Improve kfence support (mainly Hash) | expand |
Le 18/10/2024 à 19:29, Ritesh Harjani (IBM) a écrit : > copy_from_kernel_nofault() can be called when doing read of /proc/kcore. > /proc/kcore can have some unmapped kfence objects which when read via > copy_from_kernel_nofault() can cause page faults. Since *_nofault() > functions define their own fixup table for handling fault, use that > instead of asking kfence to handle such faults. > > Hence we search the exception tables for the nip which generated the > fault. If there is an entry then we let the fixup table handler handle the > page fault by returning an error from within ___do_page_fault(). > > This can be easily triggered if someone tries to do dd from /proc/kcore. > dd if=/proc/kcore of=/dev/null bs=1M > > <some example false negatives> > =============================== > BUG: KFENCE: invalid read in copy_from_kernel_nofault+0xb0/0x1c8 > Invalid read at 0x000000004f749d2e: > copy_from_kernel_nofault+0xb0/0x1c8 > 0xc0000000057f7950 > read_kcore_iter+0x41c/0x9ac > proc_reg_read_iter+0xe4/0x16c > vfs_read+0x2e4/0x3b0 > ksys_read+0x88/0x154 > system_call_exception+0x124/0x340 > system_call_common+0x160/0x2c4 > > BUG: KFENCE: use-after-free read in copy_from_kernel_nofault+0xb0/0x1c8 > Use-after-free read at 0x000000008fbb08ad (in kfence-#0): > copy_from_kernel_nofault+0xb0/0x1c8 > 0xc0000000057f7950 > read_kcore_iter+0x41c/0x9ac > proc_reg_read_iter+0xe4/0x16c > vfs_read+0x2e4/0x3b0 > ksys_read+0x88/0x154 > system_call_exception+0x124/0x340 > system_call_common+0x160/0x2c4 > > Fixes: 90cbac0e995d ("powerpc: Enable KFENCE for PPC32") > Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu> Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu> Nit below. > Reported-by: Disha Goel <disgoel@linux.ibm.com> > Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com> > --- > arch/powerpc/mm/fault.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c > index 81c77ddce2e3..316f5162ffc4 100644 > --- a/arch/powerpc/mm/fault.c > +++ b/arch/powerpc/mm/fault.c > @@ -439,10 +439,17 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address, > /* > * The kernel should never take an execute fault nor should it > * take a page fault to a kernel address or a page fault to a user > - * address outside of dedicated places > + * address outside of dedicated places. > + * > + * Rather than kfence directly reporting false negatives, search whether > + * the NIP belongs to the fixup table for cases where fault could come > + * from functions like copy_from_kernel_nofault(). > */ > if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write))) { > - if (kfence_handle_page_fault(address, is_write, regs)) > + Why do you need a blank line here ? > + if (is_kfence_address((void *)address) && > + !search_exception_tables(instruction_pointer(regs)) && > + kfence_handle_page_fault(address, is_write, regs)) > return 0; > > return SIGSEGV; > -- > 2.46.0 >
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index 81c77ddce2e3..316f5162ffc4 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -439,10 +439,17 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address, /* * The kernel should never take an execute fault nor should it * take a page fault to a kernel address or a page fault to a user - * address outside of dedicated places + * address outside of dedicated places. + * + * Rather than kfence directly reporting false negatives, search whether + * the NIP belongs to the fixup table for cases where fault could come + * from functions like copy_from_kernel_nofault(). */ if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write))) { - if (kfence_handle_page_fault(address, is_write, regs)) + + if (is_kfence_address((void *)address) && + !search_exception_tables(instruction_pointer(regs)) && + kfence_handle_page_fault(address, is_write, regs)) return 0; return SIGSEGV;
copy_from_kernel_nofault() can be called when doing read of /proc/kcore. /proc/kcore can have some unmapped kfence objects which when read via copy_from_kernel_nofault() can cause page faults. Since *_nofault() functions define their own fixup table for handling fault, use that instead of asking kfence to handle such faults. Hence we search the exception tables for the nip which generated the fault. If there is an entry then we let the fixup table handler handle the page fault by returning an error from within ___do_page_fault(). This can be easily triggered if someone tries to do dd from /proc/kcore. dd if=/proc/kcore of=/dev/null bs=1M <some example false negatives> =============================== BUG: KFENCE: invalid read in copy_from_kernel_nofault+0xb0/0x1c8 Invalid read at 0x000000004f749d2e: copy_from_kernel_nofault+0xb0/0x1c8 0xc0000000057f7950 read_kcore_iter+0x41c/0x9ac proc_reg_read_iter+0xe4/0x16c vfs_read+0x2e4/0x3b0 ksys_read+0x88/0x154 system_call_exception+0x124/0x340 system_call_common+0x160/0x2c4 BUG: KFENCE: use-after-free read in copy_from_kernel_nofault+0xb0/0x1c8 Use-after-free read at 0x000000008fbb08ad (in kfence-#0): copy_from_kernel_nofault+0xb0/0x1c8 0xc0000000057f7950 read_kcore_iter+0x41c/0x9ac proc_reg_read_iter+0xe4/0x16c vfs_read+0x2e4/0x3b0 ksys_read+0x88/0x154 system_call_exception+0x124/0x340 system_call_common+0x160/0x2c4 Fixes: 90cbac0e995d ("powerpc: Enable KFENCE for PPC32") Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu> Reported-by: Disha Goel <disgoel@linux.ibm.com> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com> --- arch/powerpc/mm/fault.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) -- 2.46.0