From: Alexandre Ghiti alexghiti@rivosinc.com
[ Upstream commit 4b05b993900dd3eba0fc83ef5c5ddc7d65d786c6 ]
It was reported that the riscv kernel hangs while executing the test in [1].
Indeed, the test hangs when trying to write a buffer to a file. The problem is that the riscv implementation of raw_copy_from_user() does not return the correct number of bytes not written when an exception happens and is fixed up, instead it always returns the initial size to copy, even if some bytes were actually copied.
generic_perform_write() pre-faults the user pages and bails out if nothing can be written, otherwise it will access the userspace buffer: here the riscv implementation keeps returning it was not able to copy any byte though the pre-faulting indicates otherwise. So generic_perform_write() keeps retrying to access the user memory and ends up in an infinite loop.
Note that before the commit mentioned in [1] that introduced this regression, it worked because generic_perform_write() would bail out if only one byte could not be written.
So fix this by returning the number of bytes effectively not written in __asm_copy_[to|from]_user() and __clear_user(), as it is expected.
Link: https://lore.kernel.org/linux-riscv/20230309151841.bomov6hq3ybyp42a@debian/ [1] Fixes: ebcbd75e3962 ("riscv: Fix the bug in memory access fixup code") Reported-by: Bo YU tsu.yubo@gmail.com Closes: https://lore.kernel.org/linux-riscv/20230309151841.bomov6hq3ybyp42a@debian/#... Reported-by: Aurelien Jarno aurelien@aurel32.net Closes: https://lore.kernel.org/linux-riscv/ZNOnCakhwIeue3yr@aurel32.net/ Signed-off-by: Alexandre Ghiti alexghiti@rivosinc.com Reviewed-by: Björn Töpel bjorn@rivosinc.com Tested-by: Aurelien Jarno aurelien@aurel32.net Reviewed-by: Aurelien Jarno aurelien@aurel32.net Link: https://lore.kernel.org/r/20230811150604.1621784-1-alexghiti@rivosinc.com Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/riscv/lib/uaccess.S | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S index ec486e5369d9b..09b47ebacf2e8 100644 --- a/arch/riscv/lib/uaccess.S +++ b/arch/riscv/lib/uaccess.S @@ -17,8 +17,11 @@ ENTRY(__asm_copy_from_user) li t6, SR_SUM csrs CSR_STATUS, t6
- /* Save for return value */ - mv t5, a2 + /* + * Save the terminal address which will be used to compute the number + * of bytes copied in case of a fixup exception. + */ + add t5, a0, a2
/* * Register allocation for code below: @@ -176,7 +179,7 @@ ENTRY(__asm_copy_from_user) 10: /* Disable access to user memory */ csrc CSR_STATUS, t6 - mv a0, t5 + sub a0, t5, a0 ret ENDPROC(__asm_copy_to_user) ENDPROC(__asm_copy_from_user) @@ -228,7 +231,7 @@ ENTRY(__clear_user) 11: /* Disable access to user memory */ csrc CSR_STATUS, t6 - mv a0, a1 + sub a0, a3, a0 ret ENDPROC(__clear_user) EXPORT_SYMBOL(__clear_user)