riscv/shstk: If needed allocate a new shadow stack on clone

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Userspace specifies CLONE_VM to share address space and spawn new
thread.  'clone' allows userspace to specify a new stack for a new
thread. However there is no way to specify a new shadow stack base
address without changing the API. This patch allocates a new shadow
stack whenever CLONE_VM is given.

In case of CLONE_VFORK, the parent is suspended until the child
finishes; thus the child can use the parent's shadow stack. In case of
!CLONE_VM, COW kicks in because entire address space is copied from
parent to child.

'clone3' is extensible and can provide mechanisms for specifying the
shadow stack as an input parameter. This is not settled yet and is
being extensively discussed on the mailing list. Once that's settled,
this code should be adapted.

Reviewed-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Tested-by: Andreas Korb <andreas.korb@aisec.fraunhofer.de> # QEMU, custom CVA6
Tested-by: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Link: https://patch.msgid.link/20251112-v5_user_cfi_series-v23-11-b55691eacf4f@rivosinc.com
[pjw@kernel.org: cleaned up patch description]
Signed-off-by: Paul Walmsley <pjw@kernel.org>

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This commit is contained in:

Deepak Gupta 2026-01-25 21:09:54 -07:00 • committed by Paul Walmsley

parent c70772afd5

commit fd44a4a855

4 changed files with 162 additions and 0 deletions

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7

arch/riscv/include/asm/mmu_context.h

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25

arch/riscv/include/asm/usercfi.h

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arch/riscv/kernel/process.c

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120

arch/riscv/kernel/usercfi.c

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