From: Greg Kroah-Hartman gregkh@linuxfoundation.org
From: Joerg Roedel jroedel@suse.de
commit bffe30dd9f1f3b2608a87ac909a224d6be472485 upstream.
The #VC handler must run in atomic context and cannot sleep. This is a problem when it tries to fetch instruction bytes from user-space via copy_from_user().
Introduce a insn_fetch_from_user_inatomic() helper which uses __copy_from_user_inatomic() to safely copy the instruction bytes to kernel memory in the #VC handler.
Fixes: 5e3427a7bc432 ("x86/sev-es: Handle instruction fetches from user-space") Signed-off-by: Joerg Roedel jroedel@suse.de Signed-off-by: Borislav Petkov bp@suse.de Cc: stable@vger.kernel.org # v5.10+ Link: https://lkml.kernel.org/r/20210303141716.29223-6-joro@8bytes.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/insn-eval.h | 2 + arch/x86/kernel/sev-es.c | 2 - arch/x86/lib/insn-eval.c | 66 ++++++++++++++++++++++++++++++--------- 3 files changed, 55 insertions(+), 15 deletions(-)
--- a/arch/x86/include/asm/insn-eval.h +++ b/arch/x86/include/asm/insn-eval.h @@ -23,6 +23,8 @@ unsigned long insn_get_seg_base(struct p int insn_get_code_seg_params(struct pt_regs *regs); int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE]); +int insn_fetch_from_user_inatomic(struct pt_regs *regs, + unsigned char buf[MAX_INSN_SIZE]); bool insn_decode(struct insn *insn, struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE], int buf_size);
--- a/arch/x86/kernel/sev-es.c +++ b/arch/x86/kernel/sev-es.c @@ -258,7 +258,7 @@ static enum es_result vc_decode_insn(str int res;
if (user_mode(ctxt->regs)) { - res = insn_fetch_from_user(ctxt->regs, buffer); + res = insn_fetch_from_user_inatomic(ctxt->regs, buffer); if (!res) { ctxt->fi.vector = X86_TRAP_PF; ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER; --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -1415,6 +1415,25 @@ void __user *insn_get_addr_ref(struct in } }
+static unsigned long insn_get_effective_ip(struct pt_regs *regs) +{ + unsigned long seg_base = 0; + + /* + * If not in user-space long mode, a custom code segment could be in + * use. This is true in protected mode (if the process defined a local + * descriptor table), or virtual-8086 mode. In most of the cases + * seg_base will be zero as in USER_CS. + */ + if (!user_64bit_mode(regs)) { + seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS); + if (seg_base == -1L) + return 0; + } + + return seg_base + regs->ip; +} + /** * insn_fetch_from_user() - Copy instruction bytes from user-space memory * @regs: Structure with register values as seen when entering kernel mode @@ -1431,24 +1450,43 @@ void __user *insn_get_addr_ref(struct in */ int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE]) { - unsigned long seg_base = 0; + unsigned long ip; int not_copied;
- /* - * If not in user-space long mode, a custom code segment could be in - * use. This is true in protected mode (if the process defined a local - * descriptor table), or virtual-8086 mode. In most of the cases - * seg_base will be zero as in USER_CS. - */ - if (!user_64bit_mode(regs)) { - seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS); - if (seg_base == -1L) - return 0; - } + ip = insn_get_effective_ip(regs); + if (!ip) + return 0; + + not_copied = copy_from_user(buf, (void __user *)ip, MAX_INSN_SIZE); + + return MAX_INSN_SIZE - not_copied; +} + +/** + * insn_fetch_from_user_inatomic() - Copy instruction bytes from user-space memory + * while in atomic code + * @regs: Structure with register values as seen when entering kernel mode + * @buf: Array to store the fetched instruction + * + * Gets the linear address of the instruction and copies the instruction bytes + * to the buf. This function must be used in atomic context. + * + * Returns: + * + * Number of instruction bytes copied. + * + * 0 if nothing was copied. + */ +int insn_fetch_from_user_inatomic(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE]) +{ + unsigned long ip; + int not_copied;
+ ip = insn_get_effective_ip(regs); + if (!ip) + return 0;
- not_copied = copy_from_user(buf, (void __user *)(seg_base + regs->ip), - MAX_INSN_SIZE); + not_copied = __copy_from_user_inatomic(buf, (void __user *)ip, MAX_INSN_SIZE);
return MAX_INSN_SIZE - not_copied; }