projects / thirdparty / kernel / stable-queue.git / blame
| Commit | Line | Data |
|---|---|---|
| c8fb49aa GKH |
1 | From e90e6fddc57055c4c6b57f92787fea1c065d440b Mon Sep 17 00:00:00 2001 |
| 2 | From: Alex Smith <alex.smith@imgtec.com> | |
| 3 | Date: Wed, 23 Jul 2014 14:40:11 +0100 | |
| 4 | Subject: MIPS: O32/32-bit: Fix bug which can cause incorrect system call restarts | |
| 5 | ||
| 6 | From: Alex Smith <alex.smith@imgtec.com> | |
| 7 | ||
| 8 | commit e90e6fddc57055c4c6b57f92787fea1c065d440b upstream. | |
| 9 | ||
| 10 | On 32-bit/O32, pt_regs has a padding area at the beginning into which the | |
| 11 | syscall arguments passed via the user stack are copied. 4 arguments | |
| 12 | totalling 16 bytes are copied to offset 16 bytes into this area, however | |
| 13 | the area is only 24 bytes long. This means the last 2 arguments overwrite | |
| 14 | pt_regs->regs[{0,1}]. | |
| 15 | ||
| 16 | If a syscall function returns an error, handle_sys stores the original | |
| 17 | syscall number in pt_regs->regs[0] for syscall restart. signal.c checks | |
| 18 | whether regs[0] is non-zero, if it is it will check whether the syscall | |
| 19 | return value is one of the ERESTART* codes to see if it must be | |
| 20 | restarted. | |
| 21 | ||
| 22 | Should a syscall be made that results in a non-zero value being copied | |
| 23 | off the user stack into regs[0], and then returns a positive (non-error) | |
| 24 | value that matches one of the ERESTART* error codes, this can be mistaken | |
| 25 | for requiring a syscall restart. | |
| 26 | ||
| 27 | While the possibility for this to occur has always existed, it is made | |
| 28 | much more likely to occur by commit 46e12c07b3b9 ("MIPS: O32 / 32-bit: | |
| 29 | Always copy 4 stack arguments."), since now every syscall will copy 4 | |
| 30 | arguments and overwrite regs[0], rather than just those with 7 or 8 | |
| 31 | arguments. | |
| 32 | ||
| 33 | Since that commit, booting Debian under a 32-bit MIPS kernel almost | |
| 34 | always results in a hang early in boot, due to a wait4 syscall returning | |
| 35 | a PID that matches one of the ERESTART* codes, which then causes an | |
| 36 | incorrect restart of the syscall. | |
| 37 | ||
| 38 | The problem is fixed by increasing the size of the padding area so that | |
| 39 | arguments copied off the stack will not overwrite pt_regs->regs[{0,1}]. | |
| 40 | ||
| 41 | Signed-off-by: Alex Smith <alex.smith@imgtec.com> | |
| 42 | Reviewed-by: Aurelien Jarno <aurelien@aurel32.net> | |
| 43 | Tested-by: Aurelien Jarno <aurelien@aurel32.net> | |
| 44 | Cc: linux-mips@linux-mips.org | |
| 45 | Patchwork: https://patchwork.linux-mips.org/patch/7454/ | |
| 46 | Signed-off-by: Ralf Baechle <ralf@linux-mips.org> | |
| 47 | Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> | |
| 48 | ||
| 49 | --- | |
| 50 | arch/mips/include/asm/ptrace.h | 2 +- | |
| 51 | 1 file changed, 1 insertion(+), 1 deletion(-) | |
| 52 | ||
| 53 | --- a/arch/mips/include/asm/ptrace.h | |
| 54 | +++ b/arch/mips/include/asm/ptrace.h | |
| 55 | @@ -23,7 +23,7 @@ | |
| 56 | struct pt_regs { | |
| 57 | #ifdef CONFIG_32BIT | |
| 58 | /* Pad bytes for argument save space on the stack. */ | |
| 59 | - unsigned long pad0[6]; | |
| 60 | + unsigned long pad0[8]; | |
| 61 | #endif | |
| 62 | ||
| 63 | /* Saved main processor registers. */ |