Messages in this thread | | | Subject | Re: [PATCH v2] powerpc/uaccess: Use flexible addressing with __put_user()/__get_user() | From | Christophe Leroy <> | Date | Wed, 1 Jul 2020 09:05:04 +0200 |
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Le 30/06/2020 à 23:18, Segher Boessenkool a écrit : > Hi again, > > Thanks for your work so far! > > On Tue, Jun 30, 2020 at 06:53:39PM +0000, Christophe Leroy wrote: >> On 06/30/2020 04:33 PM, Segher Boessenkool wrote: >>>>> + make -s CC=powerpc64-linux-gnu-gcc -j 160 >>>>> In file included from /linux/include/linux/uaccess.h:11:0, >>>>> from /linux/include/linux/sched/task.h:11, >>>>> from /linux/include/linux/sched/signal.h:9, >>>>> from /linux/include/linux/rcuwait.h:6, >>>>> from /linux/include/linux/percpu-rwsem.h:7, >>>>> from /linux/include/linux/fs.h:33, >>>>> from /linux/include/linux/huge_mm.h:8, >>>>> from /linux/include/linux/mm.h:675, >>>>> from /linux/arch/powerpc/kernel/signal_32.c:17: >>>>> /linux/arch/powerpc/kernel/signal_32.c: In function >>>>> 'save_user_regs.isra.14.constprop': >>>>> /linux/arch/powerpc/include/asm/uaccess.h:161:2: error: 'asm' operand has >>>>> impossible constraints >>>>> __asm__ __volatile__( \ >>>>> ^ >>>>> /linux/arch/powerpc/include/asm/uaccess.h:197:12: note: in expansion of >>>>> macro '__put_user_asm' >>>>> case 4: __put_user_asm(x, ptr, retval, "stw"); break; \ >>>>> ^ >>>>> /linux/arch/powerpc/include/asm/uaccess.h:206:2: note: in expansion of >>>>> macro '__put_user_size_allowed' >>>>> __put_user_size_allowed(x, ptr, size, retval); \ >>>>> ^ >>>>> /linux/arch/powerpc/include/asm/uaccess.h:220:2: note: in expansion of >>>>> macro '__put_user_size' >>>>> __put_user_size(__pu_val, __pu_addr, __pu_size, __pu_err); \ >>>>> ^ >>>>> /linux/arch/powerpc/include/asm/uaccess.h:96:2: note: in expansion of >>>>> macro '__put_user_nocheck' >>>>> __put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr))) >>>>> ^ >>>>> /linux/arch/powerpc/kernel/signal_32.c:120:7: note: in expansion of macro >>>>> '__put_user' >>>>> if (__put_user((unsigned int)gregs[i], &frame->mc_gregs[i])) >>>>> ^ >>> >>> Can we see what that was after the macro jungle? Like, the actual >>> preprocessed code? >> >> Sorry for previous misunderstanding >> >> Here is the code: >> >> #define __put_user_asm(x, addr, err, op) \ >> __asm__ __volatile__( \ >> "1: " op "%U2%X2 %1,%2 # put_user\n" \ >> "2:\n" \ >> ".section .fixup,\"ax\"\n" \ >> "3: li %0,%3\n" \ >> " b 2b\n" \ >> ".previous\n" \ >> EX_TABLE(1b, 3b) \ >> : "=r" (err) \ >> : "r" (x), "m<>" (*addr), "i" (-EFAULT), "0" (err)) > > Yeah I don't see it. I'll have to look at compiler debug dumps, but I > don't have any working 4.9 around, and I cannot reproduce this with > either older or newer compilers.
I reproduced it with 4.8.5
> > It is complainig that constrain_operands just does not work *at all* on > this "m<>" constraint apparently, which doesn't make much sense. >
Here is a small reproducer:
#include <linux/elf.h> #include <linux/ptrace.h> #include <linux/uaccess.h>
struct mcontext { elf_gregset_t32 mc_gregs; elf_fpregset_t mc_fregs; unsigned int mc_pad[2]; elf_vrregset_t32 mc_vregs __attribute__((__aligned__(16))); elf_vsrreghalf_t32 mc_vsregs __attribute__((__aligned__(16))); };
int save_general_regs(struct pt_regs *regs, struct mcontext __user *frame) { elf_greg_t64 *gregs = (elf_greg_t64 *)regs; int i;
for (i = 0; i <= PT_RESULT; i ++) { if (i == 14) i = 32; if (__put_user((unsigned int)gregs[i], &frame->mc_gregs[i])) return -EFAULT; } return 0; }
If you remove the "if i == 14 ..." you get no failure.
Preprocessor result:
int save_general_regs(struct pt_regs *regs, struct mcontext *frame) { elf_greg_t64 *gregs = (elf_greg_t64 *)regs; int i;
for (i = 0; i <= 43; i ++) { if (i == 14) i = 32; if (({ long __pu_err; __typeof__(*((&frame->mc_gregs[i]))) *__pu_addr = ((&frame->mc_gregs[i])); __typeof__(*((&frame->mc_gregs[i]))) __pu_val = ((__typeof__(*(&frame->mc_gregs[i])))((unsigned int)gregs[i])); __typeof__(sizeof(*(&frame->mc_gregs[i]))) __pu_size = (sizeof(*(&frame->mc_gregs[i]))); if (!(((unsigned long)__pu_addr) >= 0x8000000000000000ul)) might_fault(); (void)0; do { allow_write_to_user(__pu_addr, __pu_size); do { __pu_err = 0; switch (__pu_size) { case 1: __asm__ __volatile__( "1: " "stb" "%U2%X2 %1,%2 # put_user\n" "2:\n" ".section .fixup,\"ax\"\n" "3: li %0,%3\n" " b 2b\n" ".previous\n" ".section __ex_table,\"a\";" " " ".balign 4;" " " ".long (1b) - . ;" " " ".long (3b) - . ;" " " ".previous" " " : "=r" (__pu_err) : "r" (__pu_val), "m<>" (*__pu_addr), "i" (-14), "0" (__pu_err)); break; case 2: __asm__ __volatile__( "1: " "sth" "%U2%X2 %1,%2 # put_user\n" "2:\n" ".section .fixup,\"ax\"\n" "3: li %0,%3\n" " b 2b\n" ".previous\n" ".section __ex_table,\"a\";" " " ".balign 4;" " " ".long (1b) - . ;" " " ".long (3b) - . ;" " " ".previous" " " : "=r" (__pu_err) : "r" (__pu_val), "m<>" (*__pu_addr), "i" (-14), "0" (__pu_err)); break; case 4: __asm__ __volatile__( "1: " "stw" "%U2%X2 %1,%2 # put_user\n" "2:\n" ".section .fixup,\"ax\"\n" "3: li %0,%3\n" " b 2b\n" ".previous\n" ".section __ex_table,\"a\";" " " ".balign 4;" " " ".long (1b) - . ;" " " ".long (3b) - . ;" " " ".previous" " " : "=r" (__pu_err) : "r" (__pu_val), "m<>" (*__pu_addr), "i" (-14), "0" (__pu_err)); break; case 8: __asm__ __volatile__( "1: " "std" "%U2%X2 %1,%2 # put_user\n" "2:\n" ".section .fixup,\"ax\"\n" "3: li %0,%3\n" " b 2b\n" ".previous\n" ".section __ex_table,\"a\";" " " ".balign 4;" " " ".long (1b) - . ;" " " ".long (3b) - . ;" " " ".previous" " " : "=r" (__pu_err) : "r" (__pu_val), "m<>" (*__pu_addr), "i" (-14), "0" (__pu_err)); break; default: __put_user_bad(); } } while (0); prevent_write_to_user(__pu_addr, __pu_size); } while (0); __pu_err; })) return -14; } return 0; }
Christophe
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