powerpc: Save caller r3 prior to system_call_exception

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This reverts commit 8875f47b76 ("powerpc/syscall: Save r3 in regs->orig_r3
").

Save caller's original r3 state to the kernel stackframe before entering
system_call_exception. This allows for user registers to be cleared by
the time system_call_exception is entered, reducing the influence of
user registers on speculation within the kernel.

Prior to this commit, orig_r3 was saved at the beginning of
system_call_exception. Instead, save orig_r3 while the user value is
still live in r3.

Also replicate this early save in 32-bit. A similar save was removed in
commit 6f76a01173 ("powerpc/syscall: implement system call entry/exit
logic in C for PPC32") when 32-bit adopted system_call_exception. Revert
its removal of orig_r3 saves.

Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220921065605.1051927-3-rmclure@linux.ibm.com

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This commit is contained in:

Rohan McLure 2022-09-21 16:55:42 +10:00 • committed by Michael Ellerman

parent 5ba6c9a912

commit 2c27d4a419

3 changed files with 3 additions and 1 deletions

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1

arch/powerpc/kernel/entry_32.S

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2

arch/powerpc/kernel/interrupt_64.S

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1

arch/powerpc/kernel/syscall.c

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